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Assyrian tablet dealing with glass-making 

Makers of 








IN this book I have tried to tell the story of chemistry from its 
remote and obscure beginnings up to the establishment of the 
modern science by Dalton, Lavoisier, Avogadro and their con- 
temporaries. Brief sketches of subsequent developments have 
been appended in order that the reader may perceive something 
of the wonderful efflorescence of chemical progress in the nine- 
teenth and twentieth centuries, though a full treatment of this 
progress lay outside the present limits. Like the other volumes 
in this series of Makers of Science, Makers of Chemistry is 
primarily intended for the general reader, to whom a detailed 
account of the chemistry of the last hundred years would 
necessarily prove unintelligible unless he were equipped with 
more than a little technical knowledge. If my narrative enables 
those with no special scientific training to understand how the 
great and fascinating science of chemistry slowly took shape, 
until at length it was set firmly upon its present fruitful course, 
I shall have achieved the object with which I set out. 

Though I have had very large recourse to original authorities, 
I do not claim to have used no other. Students of the history of 
chemistry will recognize my debt to Kopp, Hoefer, Ferguson, 
Thomson, Stillman, von Meyer, von Lippmann, Berthelot and 
other scholars, which indeed I frankly and gratefully acknow- 
ledge. Unfortunately, the new discoveries concerning the works 
of Jabir ibn Hayyan, announced a short time ago by Ruska and 
his collaborators, came too late for me to make use of them ; but 
it is still uncertain what their true import may be. 

I have much pleasure in expressing my sincere thanks to the 
Delegates of the Clarendon Press and their officers for their 
continued encouragement and special assistance in the problems 
of illustration and printing; to Mr. R. B. Pilcher, Registrar of 
the Institute of Chemistry, who generously gave me the benefit 
of his unrivalled knowledge of portraits of chemists and kindly 
supplied several prints and photographs for reproduction; to 

x Preface 

Mr. W. L. Cooper, Librarian of the University of Bristol, 
for assistance in procuring journals and works of reference ; to 
Messrs. Edward Arnold & Co., who kindly gave me permission 
to quote passages from my Inorganic Chemistry in the section 
on the structure of the atom; and to Miss Lilian Long, who 
prepared the index of names, assisted in the preparation of the 
subject-index, made a typescript of the manuscript and read 
the proofs. 

Several of the illustrations are reproduced from originals in 
the Stone Memorial Science Library of Clifton College, which 
is fortunate in possessing a large and valuable collection of 
alchemical and early chemical books and manuscripts. 

E.J. H. 

Clifton College, 
February 1931. 



i . Fancy and Fable ....... i 

2- Egypt 2 

3. Sumer, Assyria, Babylonia . . . . . .10 

4. Greece . . . . . . . . 15 

5. The Classical Atomic Theory . . . . .21 

6. China ......... 24 

7. India ......... 26 

8. Rome ......... 27 

9. The Ley den and Stockholm Papyri .... 29 

10. The School of Alexandria . . . . . .32 

11. Gnosticism ........ 33 

12. Neo-Platonism . . . . . . . -33 

13. The Fusion of Practice with Speculation ... 34 

14. Zosimos the Panopolitan ...... 35 

15. A Retrospect ........ 39 

1 6. The Rise of Islam ....... 41 

17. The Origins of Alchemy in Islam . . . .43 

1 8. Jabir ibn Hayyan ....... 49 

19. The Latin Works of Jabir or Geber . . . .60 

20. Raxi ......... 63 

21. Abu Mansur Muwaffak ...... 67 

22. Avicenna ........ 68 

23. 'The Sage's Step' ....... 77 

24. Later Writers . . . . . . . .81 

25. General Review of Muslim Chemistry .... 82 

26. The Translators ....... 84 

27. Robert of Chester 86 

28. Vincent de Beauvais ....... 89 

29. Albertus Magnus and Roger Bacon .... 90 

30. Popular Books and the Technical Tradition ... 98 

31. Paracelsus ........ 106 

32. Later latrochemists . . . . . . 115 

33. van Helmont . . . . . . . .119 

xii Contents 


34. Nicolas Lemery . . . . . . .124 

35. Review of Chemistry to the Time of Lemery . . 132 

36. Robert Boyle . . . . . . . .132 

37. Becher and Stahl . . . . . . 143 

38. Troublesome Facts . . . . . . .150 

39. Mayow . . . . . . . . 154 

40. Pneumatic Chemistry . . . . . .158 

41. Joseph Black ........ 164 

42. Joseph Priestley . . . . . . .169 

43. Henry Cavendish . . . . . . .177 

44. Karl Wilhelm Scheele 186 

45. Guillaume Francois Rouelle . . . . .189 

46. Summary . . . . . . . 197 

47. Antoine Laurent Lavoisier . . . . . 197 

48. The Revision of Nomenclature . . . . .213 

49. Sir Isaac Newton . . . . . . .217 

50. John Dalton . . . . . . . .221 

51. Berzelius ......... 240 

52. Avogadro ......... 248 

53. Modern Chemistry Established ..... 257 

54. The Electrochemical or Dualistic Theory . . . 258 

55. The Classification of the Elements .... 263 

56. The Rise of Organic Chemistry ..... 273 

57. The Rise of Physical Chemistry ..... 284 

58. The Structure of the Atom . ..... 290 


Assyrian tablet dealing with glass-making. British Museum. Frontispiece 
An Alchemical Laboratory, from the fresco by Jan Stradanus. 

Photograph Alinari . . . . xvi 

1. Thoth 3 

2. An Egyptian Metallurgist. From Garland and Bannister, Ancient 

Egyptian Metallurgy (Charles Griflin Co.) .... 4 

3. Metal-workers' workshop in Egypt. From J. II. Breasted, A His- 

tory of Egypt, 2nd edition (Charles Scribner's Sons, New York; 
Hodder & Stoughton, Ltd., London) ..... 5 

4. Egyptian Goldsmiths' workshop in the Pyramid Age. From J. R. 

Partington, Everyday (Ihemntry (Macmillan & Co , Ltd.). . 7 

5. Clay Crucible found at El Argar. British Museum ... 9 

6. The oldest stone weight (Sumerian). Ashmolean Museum. . n 

7. Aristotle. Capitolme Museum, Rome. Photograph, Anderson . 17 

8. Democntus. Capitolme Museum, Rome. Photograph, Anderson . 23 

9. The Iron Pillar of Delhi. From a photograph kindly lent by Sir 

Robert I ladneld 26 

10. Pliny offering a work to Caesar. From G. Carbonelh, Sulle Fonti 

Stonchc dellti (Ihnnna e delV Alcluima in Italia, 1925 (Institute) 
Nazionale Medico-Farmacologico, Rome) . . . .28 

11. Part of the Stockholm Papyrus. From A. Lagereantz, Papyrus 

Graetus Hohniem*is (Otto Harrasowitz, Leipzig) . . .31 

12. Figures of late Greek chemical apparatus. From Berthelot, Collec- 

tion des anciens alchimiites greis, 1887 (Georges Stemheil, Pans) . 37 

13. Cleopatra's system of gold-making. From Berthelot, op. cit. . 40 

14. The Ka'ha at Mecca. By permission from a photograph by H. 

Campbell .......... 45 

15. Page of an Ancient Koran. Bodleian, MS. Marsh 2 . . .47 

16. Imaginative portrait of Jabir. Photograph, A. Chelazzi, Florence . 51 

17. The Islamic Empire ........ 53 

18. Page of one of Jabir's chemical works in arable. Bodleian, MS. 

Marsh 70 ..... .... 54 

19. Figures of alchemical processes in Arabic manuscript. British 

Museum, MS. Add. 25724 ....... 55 

20. Early MS. of Geber's Investigation of Perfection. Bodleian, MS. 

Cod. Canon, eccles. lat. 53 . . . . . . .62 

21. Title-page of A vicenna's Canon of Medicine . 71 

22. The Alhambra . . . . % 86 

23. The supposed first work on Alchemy in Latin. Bodleian, MS. 

Digby 162. . . . . . . . . -87 

24. Vincent de Beauvais. Bibliotheque Nationale, MS. Fran9ais 316 . 89 

25. Roger Bacon with a pupil. MS. Bodl. 211 . . . -93 

26. Roger Bacon's Study. From a drawing in the Bodleian Library . 95 

xiv List of Illustrations 

27. Incipit page of a fifteenth-century edition of Bartholomew's On the 

Properties of Things ........ 99 

28. Paracelsus From a painting by Rubens. . . .107 

29. Libavius' Chemical House .... .116 

30. Plan of Libavius' Chemical House . 117 

31. van Ilelmont and his Son ... . . 121 

32. Chemical Laboratory of Pieter Breughel, 1558 .... 123 

33. Nicolas Lemery. From the collection of Mr. R. B. Pilcher, O.B.E. 124 

34. Title-page of Lefebure's Trmte de la Chymie, 1669 . . . 125 

35. Apparatus from Lemery 's Course of Chymntry . . . .126 

36. Further apparatus from Lemery's Course of Chvmistry . . 127 

37. Title-page of Lemery's Course of Chvmistry . . . .129 

38. Robert Boyle. From the portrait by F. Kerseboom in the posses- 

sion of the Royal Society . . . . . . .135 

39. Title-page of The Sceptical Chymist . . ... 139 

40. The Old Ashmolean. From a print in the Bodleian Library . . 141 

41. Johann Joachim Becher. British Museum .... 144 

42. Title-page of Becher's Physica Subterranea .... 145 

43. Georg Ernst Stahl. From the collection of Mr. R. B. Pilcher, O.B.E. 147 

44. Richard Watson . . . . . . . . .149 

45. John Mayow . . . 155 

46. Apparatus of Mayow . . . ... 157 

47. Jean Bernouilli ....... .158 

48. Bernoulli's apparatus . . . . . . . .159 

49. The Rev. Stephen Hales. From the painting by T. Hudson in the 

National Portrait Gallery . . . . . . .161 

50. Stephen Hales' apparatus for collecting gases . . .162 

51. Boerhaave ...... . . 163 

52. William Cullen ..... .164 

53. Joseph Black . . . 165 

54. Joseph Priestley ... ..... 170 

55. The Birmingham mob wrecking Priestley's House. From T. E. 

Thorpe, Joseph Priestley (J. M. Dent & Sons, Ltd.) . . 171 

56. Priestley's Apparatus . . . . . . .173 

57. Autograph letter of Joseph Priestley. Science Library, Clifton 

College ......... 174-5 

58. Henry Cavendish ......... 178 

59. Cavendish's Eudiometer. Preserved in the Chemical Department, 

University of Manchester . . . . . . 179 

60. Cavendish's metallic Eudiometer . . . . . .182 

61. Cavendish's Apparatus . . . . . . . .183 

62. Guillaume Francois Rouelle. From the collection of Mr. R. B. 

Pilcher, O.B.E 191 

63. MS. of Rouelle 's Lectures. Clifton College Science Library . 192 

64. MS. of Rouelle's Lectures. Clifton College Science Library . 193 

List of Illustrations xv 

65. Le Jardin des Plantes, Paris. Photograph, E.N.A. . . . 195 

66. Antoine Laurent Lavoisier . . . . . . .198 

67. M. and Mme. Lavoisier in their laboratory. Photograph, Giraudon 199 

68. Lavoisier's Apparatus ........ 205 

69. C. L Berthollet ......... 213 

70. Sir Isaac Newton. From an engraving by S. Freeman after the 

painting by Sir Godfrey Kneller . . . . . .218 

71. Blake's Newton. From the copy in the possession of Mr. W. 

Graham Robertson, R.B.I. . . . . . . .219 

72. John Dalton . . . . . . . . .221 

73. Dalton 's card. From II. E. Roscoe,jW/w 7)//0/i(Cassell& Co., Ltd.) 223 

74. Copy of letter from Dalton to Miss Johns. From Roscoe, op. cit. . 225 

75. Some of Dalton 's Apparatus. In the possession of the Manchester 

Literary & Philosophical Society ...... 226 

76. More of Dalton 's Apparatus. In the possession of the Manchester 

Literary & Philosophical Society ...... 227 

77. Thomas Thomson ......... 228 

78. Title-page of Dalton 's A New System of Chemical Philosophy . 229 

79. Johann J. Berzehus. From Seidhtz, Portratzverk, vol. x (F. 

Bruckmann, A.-G., Munchen) . . . . . .241 

80. Dalton 's Symbols ......... 243 

81. Amedeo Avogadro From Opere stelte di Amedeo Avogadro (R. 

Accademia delle Scienze di Torino) ..... 249 

82. Joseph-Louis Gay-Lussac. From Seidlitz, op. cit. . . .251 

83 . Specimen of Avogadro 's handwriting. From Opere scelte di Amedeo 

Avogadro (R. Accademia delle Scienze di Torino) . . . 255 

84. Sir Humphry Davy. From the painting after Sir T. Lawrence in 

the National Portrait Gallery ...... 260 

85. Davy's Battery preserved in the Royal Institution . . . 261 

86. Stamslao Cannizzaro. From J. R. Partington, Everyday Chemistry 

(Macmillan Co., Ltd.) ....... 265 

87. Cannizzaro 's autograph. Science Library, Clifton College . . 266 

88. Title-page of Newlands' The Discovery of the Periodic Law, 1884 

(E. & F. N. Spon). From the copy in the Science Library, Clifton 

College .......... 267 

89. MendeleefT. Photograph, E.N.A. ...... 269 

90. Justus von Liebig. From the collection of Mr. R. B. Pilcher, O.B.E. 277 

91. Kekule. From the collection of Mr. R. B. Pilcher, O.B.E. . . 279 

92. van't HofT. From the collection of Mr. R. B. Pilcher, O.B.E. . 285 

93. Arrhemus. From the collection of Mr. R. B. Pilcher, O.B.E. . 287 

94. Crookes' Tube. From E. J. Holmyard, Inorganic Chemistry 

(Edward Arnold & Co., Ltd.) ...... 291 

95. X-ray Spectrometer. From E. J. Holmyard, op. cit. . . . 293 

96. Lattice of potassium chloride. From E. J. Holmyard, op. cit. . 295 

97. X-ray Spectra. From M. Siegbahn, The Spectroscopy of X-rays . 299 

98. Isotopes and Heterotopes. From E. J. Holmyard, op. cit. . . 301 

An Alchemical Laboratory, from the fresco by Jan Stradanus 

i . Fancy and Fable 

WE read in Genesis that 'the sons of God saw the daughters of 
men, that they were fair; and they took them wives of all which 
they chose'. From whence it was inferred, says Boerhaave, that 
the sons of God were daemons, consisting of a soul, and a 
visible, but impalpable body, like the image in a looking-glass; 
that they knew all things, fell in love with women, and revealed 
secrets. The solemn Tertullian, in a manner worthy of his (pro- 
bably apocryphal) credo quia absurdum, gravely assures us that 
these wicked angels condemned of God first discovered the art of 
painting the eyebrows, that of dyeing, and those alluring things 
gold and silver. Such an ingenious exegesis may prepare us for the 
clouds of tradition that enwrap the veritable origins of chemistry. 
Legends were invented, during the Dark and Middle Ages, to 
meet the needs of the moment : Greeks of Alexandria ascribed 
the birth of chemistry to Egypt and particularly to the god 
Thoth or Hermes ; Muslim chemists vacillated between the Pro- 
phet Muhammad and the Caliph Ali on the one hand and Aristotle, 
Plato, Pythagoras and Democritus on the other; early Jewish 
and Christian writers made the first chemists of scriptural figures ; 
and the Chinese asserted that chemistry was an outgrowth of the 
venerable system of Tao-ism. 

The extent to which the manufacture of mythical history 
proceeded may be gauged by a description of a few typical 
instances. Thus Moses, from his treatment of the golden calf, 
which could not have been accomplished (says the legend) 
without a knowledge of the art of chemistry, was elected 
a member of this strange chemical society. His sister Miriam 
was credited with the invention of the water-bath. Tubal-Cain 
was a past master in the science of the chemistry of metals. 
Cleopatra, who dissolved pearls in vinegar, was from that very 
fact declared to be an adept. The golden fleece, which Jason and 
the Argonauts carried over the Pontic Sea to Colchis, was only 
a manuscript on parchment, teaching the manner of making 

2613-4 B 

2 Egypt 

gold by chemical art. Hermes wrote 36,000 books on chemistry, 
and the inscriptions in the pyramids and tombs of Egypt are 
nothing more than pictorial representations of the transmuta- 
tion of base metals into gold. A twelfth-century hymn, by 
Adam de St. Victor, celebrates St. John the Evangelist's 
alchemical skill : 

Cum gemmarum paries fractas 

Solidasset, has compactas 

Tribuit pauperibus. 

Inexhaustum fert thesaurum, 

Qui de virgis fecit aurum, 

Gemmas de lapidibus. 

Finally, the Song of Solomon is an alchemical treatise, and 
chemistry is so called because it was invented by Noah's son 
Shem or Chem! 

2. Egypt 

LEAVING behind us these bewildering fables, let us turn to the 
more solid results of modern archaeological and historical re- 
search. Chemistry is a science that deals essentially with the 
changes in composition that matter may undergo, and therefore 
presupposes, as its necessary foundation, an accumulation of 
observational and experimental facts. These facts need not be, 
and in point of actual development were not, investigated with 
the object of elaborating a distinct scientific philosophy. They 
were rather the outcome of the various arts and crafts practised 
by the nations of antiquity, and therefore remained a hetero- 
geneous collection until informed, centuries if not millennia 
later, by the first primitive chemical theories. 

So far as our information goes, one of the oldest civilizations 
was that of ancient Egypt, which emerges from pre-history into 
the period of more or less precise chronological record at a date 
perhaps not far removed from 3400 B.C. This highly developed 
but in many respects static civilization endured for over 3,000 
. years, during which it spread its influence far and wide; some 
archaeologists, indeed, claim to see in all other civilizations the 
signs of an Egyptian origin. However this may be, it is univer- 

Egypt 3 

sally agreed that in technical arts Egyptian workers pointed the 
way to the rest of the world, and it is to them that we must turn 
for the first disco very of those facts that make chemistry possible. 
Primitive arts that provide data of a chemical nature are those 
of the metallurgist, the 
glass-maker, the dyer and 
the like, many of which 
reached an astonishingly 
high level of perfection in 
ancient Egypt. Metallurgy 
in particular was carried on 
with an elaborate technique 
and a business organization 
not unworthy of the modern 
world, while the systematic 
exploitation of mines was an 
important industry employ- 
ing many thousands of 
workers. Even as early as 
3400 B.C., at the beginning 
of the historical period, the 
Egyptians had an intimate 
knowledge of copper ores 
and of processes of extracting the metal. During the fourth 
and subsequent dynasties (i.e. from about 2900 B.C. onwards), 
metals seem to have been entirely monopolies of the Court, 
the management of the mines and quarries being entrusted 
to the highest officials and sometimes even to the sons of the 
Pharaoh. Whether these exalted personages were themselves 
professional metallurgists we do not know, but we may at 
least surmise that the details of n^etallurgical practice, being 
of extreme importance to the Crown, were carefully guarded 
from the vulgar. And when we remember the close association 
between the Egyptian royal family and the priestly class we 
appreciate the probable truth of the tradition that chemistry 
first saw the light in the laboratories of Egyptian priests. 

B 2 

Fig. i. THOTH 

In addition to copper, which was mined in the eastern desert 
between the Nile and the Red Sea, iron was known in Egypt 
from a very early period and came into general use about 
800 B.C. According to Lucas, iron appears to have been an 

Asiatic discovery. It was 
certainly known in Asia 
Minor about 1300 B.C., for 
one of the Kings of the 
Hittites sent Rameses II, 
the celebrated Pharaoh of 
the Nineteenth Dynasty, 
an iron sword and a promise 
of a shipment of the same 
metal . The Egyptians called 
iron 'the metal of heaven' 
or ba-en-pet, which in- 
dicates that the first speci- 
mens employed were of 
meteoric origin. As we 
shall see shortly, the Baby- 
lonian name has the same 
meaning. It was no doubt 
on account of its rarity that 
iron was prized so highly 
by the early Egyptians, while its celestial source would have 
added to its fascination. Strange to say, it was not used for 
decorative, religious or symbolical purposes, which coupled 
with the fact that it rusts so readily may explain why com- 
paratively few iron objects of early dynastic age have been 
discovered. One which fortunately has survived presents 
several points of interest : jt is an iron tool from the masonry 
of the Great Pyramid of Khufu at Gizeh, and thus pre- 
sumably dates from the time when the Pyramid was being 
built, i.e. about 2900 B.C. This tool was subjected to chemical 
analysis and was found to contain combined carbon, which 
suggests that it may have been composed of steel. Two other 


Egypt 5 

specimens of early Egyptian iron, when tested by Garland, also 
proved to be steely, one of them being mild steel of good quality. 
By 666 B.C, the process of case-hardening was in use for the 
edges of iron tools, but the story that the Egyptians had some 
secret means of hardening copper and bronze that has since 
been lost is probably without foundation. Desch has shown 
that a hammered bronze, containing 10*34 P er cen t- f tin, is 


considerably harder than copper and keeps a cutting edge much 

Of the other non-precious metals, tin was used in the manu- 
facture of bronze, and cobalt has been detected as a colouring 
agent in certain specimens of glass and glaze. Neither metal 
occurs naturally in Egypt, and it seems probable that supplies of 
ore were imported from Persia. Lead, though it never found 
extensive application, was among the earliest metals known, 
specimens having been found in graves of pre-dynastic times. 
Galena (PbS) was mined in Egypt at Gebel Rasas (' Mountain 
of Lead'), a few miles from the Red Sea coast; and the supply 
must have been fairly good, for wheri the district was re-worked 
from 1912 to 1915 it produced more than 18,000 tons of ore. 

The vast quantities of gold amassed by the Pharaohs were the 
envy of contemporary and later sovereigns. Though much was 
imported, received by way of tribute, or captured in warfare, 
the Egyptian mines themselves were reasonably productive. 

6 Egypt 

Over one hundred ancient gold workings have been discovered 
in Egypt and the Sudan, though within the limits of Egypt 
proper there appear to have been gold mines only in the desert 
valleys to the east of the Nile near Koptos, Ombos and Apolli- 
nopolis Magna. Of one of these mines possibly near Apolli- 
nopolis a plan has been found in a papyrus of the fourteenth 
century B.C., and the remains of no fewer than 1,300 houses for 
gold-miners are still to be seen in the Wadi Fawakhir, half-way 
between Koptos and the Red Sea. In one of the treasure 
chambers of the temple of Rameses III, at Medinet-Habu, are 
represented eight large bags, seven of which contained gold and 
bear the following descriptive labels : 


Ethiopian gold. 
T Gold, 1000 ten. 

_, , Gold of the mountain, 
iv. P*""*! ^^ ^T T Alluvial gold, 1000 ten. 

/WWW WVWA I 1 ^ O 

v> p^ 1 n Gold from Apollinopolis Magna. 

/WWVA ~"7. ^xl [\>^yl A 

vi. P^ fi) tj() ^ Gold from Ombos. 
vii. C^^\ 5 J Gold from Koptos. 

The Egyptian word for gold is nub y which survives in the 
name Nubia, a country that provided a great deal of the precious 
metal in ancient days. The symbol for nub, f^H, has given rise 
to much speculation and many different interpretations have 
been suggested. Champollion regarded it as a kind of crucible, 
while Rossellini and Lepsius preferred to see in it a bag or cloth, 
with hanging ends, in which the grains of gold were washed 
the radiating lines representing the streams of water that ran 
through. Crivelli has more recently advanced the theory that 
P^O is the conventional sign for a portable furnace used for the 
fusion of gold, and that the rays represent the flames, which, 'as 

Egypt 7 

can be observed in the use of this type of furnace, are unable to 
ascend because the wind inclines them horizontally'. In the 
later dynasties, the Egyptians themselves forgot the original 
signification of the sign and drew it as a necklace with pendent 
beads, though Elliot Smith says that this was the primitive form 


and became the determinative of Hathor, the Egyptian Aphro- 
dite, who was the guardian of the Eastern valleys where gold 
was found. 

The gold mines in Nubia and other parts of the Egyptian 
empire seem to have been very efficiently designed and con- 
trolled, though with a callous disregard for the human element 
employed. This is the picture which is drawn for us by Dio- 
dorus Siculus (following Agatharchides of Cnidos) : 

In the furthest part of Egypt, on the confines of Arabia and 
Ethiopia, there is a place containing many mines of gold, which is 
procured by numerous workmen with vast hardship and expense. 
J The soil being naturally^ black, and containing many veins and 
strata of marble, extremely white, and thus distinguished from the 
circumjacent materials, the superintendents set over the mine- 
works prosecute the search with a multitude of labourers. For the 
kings of Egypt collect those condemned for crimes, captives taken 
in war, persons ruined by false accusations, and therefore sen- 

8 Egypt 

tenced to imprisonment, sometimes alone, sometimes with all their 
families, and condemn them to the mines, thereby at once inflict- 
ing punishment upon the sentenced, and extracting vast profits out 
of their labours. Now these convicts, in great numbers, all in 
fetters, are kept at the works, not merely all day, but throughout 
the night also, getting no intermission of labour, and carefully 
guarded against escaping. For guards are set over them of foreign 
soldiers, and speaking a different language, so that it is impossible 
for the prisoners to corrupt any of their guards by speech, or by 
motives of humanity. The ground containing the gold they first 
heat with long-continued fire, and so render full of fissures, before 
they apply manual labour to it ; but the rock that is soft and capable 
of yielding to moderate labour is cut down with the tools stone- 
cutters use by myriads of these poor wretches. The entire opera- 
tion is directed by the engineer, who looks out for the proper stone, 
and marks it out for the labourers. Of those appointed to this 
miserable task, such as are of the strongest break down the marble- 
like rock with iron pickaxes, applying no art to their labour, but 
mere brute strength, and thus cut galleries, running not in a 
straight line, but guided by the direction of the white veins. 
These men, in consequence of the crooked course of the galleries, 
work in darkness, and therefore carry lamps ingeniously fastened 
upon their foreheads; and frequently changing their posture, 
according to the arrangement of the veins, they break down and 
bring to the floor the fragments of the cut rock, doing this under 
the lash and cruelty of an overseer. Meanwhile the boys, creeping 
into the passages, throw up, with much toil, the broken mineral as 
it falls little by little, and carry it up into the open air at the mine's 
mouth. Here those above thirty years old receive from them a 
fixed measure of the broken ore, and pound it in stone mortars 
with iron pestles, until they reduce it to the size of a vetch. From 
these the granulated ore is taken by the women and the older men, 
who have many hand-mills set in a row, and, standing two or three 
together at the handle, they (grind the measure given to them as fine 
as flour. 

Last of all the skilled workmen receive the ore ground fine, and 
complete the operation. They have a board placed somewhat 
sloping, on which they throw a small quantity of the dust, and 
pouring water over it they rub it. Then the earthy particles are 

Egypt 9 

dissolved by the water, and run off, owing to the slope of the board ; 
but those containing the gold remain upon it in consequence of 
their weight. Repeating this frequently, first of all they rub the 
dust gently with their hands, afterwards they press it with coarse 
sponges lightly, taking up in this way the loose and earthy part, 
until the gold-dust is left behind unmixed. Finally, other work- 
men, taking from them the collected dust, according to weight and 


measure, place it in earthen crucibles, mixing in a certain propor- 
tion of lead-ore and lumps of salt, to which they add a little tin and 
barley-bran. Then they fit on the cover of the crucible, luting it 
down carefully with clay, and bake it in a furnace five days and 
nights continuously. Then taking it out, and leaving it to cool, 
they find nothing of the other materials left in the crucible, but get 
the gold quite pure, but slightly diminished in weight. The dis- 
covery of these mines dates very far back; probably they were 
found out by the ancient kings. 

Alluvial auriferous sand was also treated, a distinction being 
made between the gold obtained in this way and that extracted 
from the mines. The latter was called nub-en-set, i.e. 'gold of the 
mountain', while alluvial gold was named nub-en-mu, i.e. 'gold 
of the river'. Auriferous sand was placed in a bag made of a 

io Sumer, Assyria, Babylonia 

fleece with the woolly side inwards ; water was then added and 
the bag vigorously shaken by two men. When the water was 
poured off, the earthy particles were carried away, leaving 
the heavier particles of gold adhering to the fleece. There is a 
picture of this operation on one of the buildings at Thebes. 

Metallurgy was by no means the only art practised with con- 
spicuous success by the ancient Egyptian craftsmen. Glass was 
almost certainly the invention, not of the Phoenicians, but of the 
Egyptians, and was produced on a large scale from a very early 
date. Artificial pearls, made of glass, were manufactured in such 
numbers that they formed an important article of export trade, 
and the old legends of enormous emeralds and other precious 
stones are most reasonably explained on the assumption that the 
preparation of paste jewelry was widely undertaken. The 
earliest glass-works of which the remains have been found date 
from the eighteenth dynasty, and the oldest dated glass object 
is a large ball bead bearing the cartouche of Amen-Hotep I, 
now in the Ashmolean Museum at Oxford. The invention of 
glass-blowing, as opposed to the older method of glass-moulding, 
is comparatively recent, dating back only to about the beginning 
of the Christian Era. Sir Flinders Petrie has shown that the 
reliefs at Beni-Hassan, which were formerly supposed to 
represent glass-blowers, are more probably to be interpreted as 
metal-workers blowing a fire. 

The manufacture of soap (from oil and naturally-occurring 
sodium sesqui-carbonate or natron), the art of dyeing (including 
the use of alum as a mordant), the preparation of enamels, 
poisons, perfumes, unguents and cosmetics: such were some of 
the minor technical arts that flourished in Egypt. They all 
imply an acquaintance with the chemical properties of a very large 
number of compounds, an d^the Egyptians thus provided the first 
basis for chemistry and established the first chemical industry. 

3. Sumer, Assyria, Babylonia 

THE banks of the Tigris and Euphrates witnessed the growth 
and decay of at least three ancient civilizations, namely those of 

Sumer, Assyria, Babylonia n 

Sumer, Assyria, and Babylonia. Four or five millennia before 
Christ, the southern part of Babylonia was inhabited by a non- 
Semitic race known as the Sumerians, who were probably 
immigrants from the east and north-east. Professor S. H. 
Langdon believes that a great pre-historic civilization spread 
from Central Asia to the plateau of Iran (ancient Persia), and to 
Syria and Egypt, long before 4000 B.C., and that the Sumerian 


people, who were a somewhat later branch of the Central Asian 
people, entered Mesopotamia before 5000 B.C. 

The earliest archaeological remains of the Sumerians are 
found in the mound that represents the ancient town of Susa, 
in Elam. They show us that this people brought with them, or 
very quickly discovered, the use of metals, for among the articles 
discovered are rude copper objects. It seems likely, too, that 
to the Sumerians is due the invention of writing, which was 
originally pictorial. The use of the clay tablet so characteristic 
of ancient Mesopotamian civilization appears to have origi- 
nated about a century before the time of the oldest historical ruler 
of the town of Lagash (the modern mound Telloh), whose name 
was Ur-Nina and who lived about 3100 B.C. The reign of 
Entemena, Ur-Nina's great-grandson (c. 3040 B.C.), is of particu- 

12 Sumer, Assyria, Babylonia 

lar interest to us, because in it were made the two oldest known 
stone weights. One of these is preserved in the Ashmolean 
Museum at Oxford. It has a unique form, being pear-shaped, 
with a deep groove on each side running from the point to the 
base, and is highly polished. The top is pierced by a round hole 
by which the weight was suspended. The object weighs 
680-485 grams (about if Ib.) and carries the following inscrip- 
tion in ancient Sumerian characters: 'One mana of wages in 
wool. Dudu the High-Priest. ' Dudu, high-priest of the god 
Nin-girsu, was a very important official in the city of Lagash 
during Entemena's reign. Monuments of this king were, in fact, 
frequently dated by the phrase, 'At this time his servant Dudu 
was high-priest of the god Nin-girsu'. 

Even in the earliest period, anterior to the reign of Ur-Nina, 
the Sumerians practised the art of casting in metal, small 
foundation-figures having been discovered that were cast in 
solid copper. This was the metal most frequently employed by 
the Sumerians, who seem to have been unacquainted with 

After a long period, the Sumerians were overcome by the 
Semites, who adopted the culture of their predecessors. The 
celebrated Sargon, king of Akkad (the northern portion of Baby- 
lonia), about 28728.0., was a great warrior, and among other 
conquests in the third year of his reign invaded the West and 
may even have penetrated to Cyprus. An inscription on one of 
his statues says : 'The god Enlil gave unto him the upper land, 
Maer, Yarmuthi and Ibla, as far as the cedar forests and 
the silver-mountains/ The latter are probably the Taurus 
mountains, and the inscription bears witness to the great age 
of silver-mining in Asia Minor. 

In the reign of Gudea, ruler of Lagash (c. 2600), gypsum and 
asphalt were brought by ship from Magda, while copper was 
obtained from the neighbouring city of Rimash (in the foothills 
of the Zagros mountains). His gold Gudea procured from 
Melukhkha, and his silver from Taurus, while his marble he 
quarried in the 'Amorite mountains' (Anti- Lebanon?). 

Sumer, Assyria, Babylonia 13 

The golden age of Babylon was under Khammurabi (^123- 
2081 B.C.), who is well known for his famous Code of Law. In 
his time, gold, silver, copper and lead were all mined and were 
in common use. The copper- working industry was carried on 
at Umma principally, but Dur-gurgurri, near Larsa, 'was 
another town where the clangour of coppersmiths at work could 
be heard continuously/ In the first volume of the Cambridge 
Ancient History, we read that a private letter of the period of the 
first Babylonian Dynasty (founded about 2200 B.C.) runs as 
follows: 'To Baba say: thus Munaivirum. May Shamash and 
Marduk keep thee in good health for ever. I am sending 
Lumursha-Marduk ; give him a copper pot. I am out of health : 
since thou lovest me truly, send the copper pot/ *It is an 
indication that a copper bazaar existed only in the towns, as of 
course happens to this day/ 

During the second millennium B.C., the high-priests of the 
northern city of Assur became kings, and so the new kingdom of 
Assyria arose. At first, Babylonia exacted tribute from Assyria, 
but in 1250 B.C. the Assyrian king Tiglath-Inurta captured 
Babylon and ruled it for seven years. He was afterwards driven 
out, and subsequently murdered by his own son, but for many 
years Assyria was supreme. Not until the time of Nebuchad- 
rezzar did Babylonia regain its ancient power. In 668 B.C. the 
king of Assyria was Assurbanipal, the Sardanapallos of the 
Greeks. He was a generous patron of literature and learning and 
possessed an immense library. No fewer than 25,000 tablets 
from it have been excavated, and are now in the British Museum. 
Among them are several that deal with glass-making from 
a severely practical point of view and these are of great 
interest to students of the history of chemistry. They have 
found a very capable interpreter in t\ie person of Dr. R. Camp- 
bell Thompson, who has not only edited and translated the 
texts, but has provided us with a remarkably ingenious and 
penetrating commentary. 

The essentials in all glass-making are silica, an alkali, and 
lime or, less frequently, lead oxide. A decolourizing agent, such 

14 Sumer, Assyria, Babylonia 

as manganese dioxide, is usually added. That all these sub- 
stances were used so far back as A.D. 79 is proved by an analysis 
of window-glass from Pompeii: silica, 69; soda, 17; lime, 7; 
alumina, 3 ; iron oxide, i per cent. ; manganese and copper, traces. 
Chemical analysis of ancient glasses has, moreover, revealed the 
nature of many of the colouring agents employed in the manu- 
facture of tinted glass ; thus Assyrian blue glass has been found 
to contain copper, and red glass cuprous oxide. Assyrian white 
glass contains tin oxide, while lead antimonate has been dis- 
covered in yellow. 

From data of this kind it becomes an easier task to identify 
the names of the principal constituents of Assyrian glass as 
given in the texts. Uhulu, immanakku and namrutu are the basic 
substances. The first, uhulu, has long been recognized as 
'alkali', and Dr. Thompson is able to show that immanakku 
probably represents a pure quartz sand. Since the word for lead 
(anaku) does not occur in any of the glass-texts, it is reasonable 
to assume that namrutu signifies a form of lime or limestone, 
and the evidence shows that it is probably chalk. With the 
three main ingredients definitely settled, attention can be devoted 
to the rest, and one of the most interesting recipes appears 
to describe a rudimentary form of the Purple of Cassius. The 
aim of the operation described in this particular recipe is 
apparently to produce an artificial pink or red coral. The in- 
gredients are given as 7,200 parts of an ordinary glass, 32 parts 
of oxide of tin, 20 parts of antimony, an unreadable number of 
parts of salt or saltpetre, and i part of gold. The proportion 
of gold here stated (0-014 per cent.) is of the usual order of 
magnitude in the preparation of ruby glass. 

Several of the technical terms are of great interest, such as 
guhlu (eye-paint), whence^ the Arabic kuhl and our alcohol', 
sindu arqu (yellow paint), whence sandarach; sadanu, whence the 
Arabic shadana, haematite. Sapphire is traced back to the 
Assyrian sipru, and means 'the scratching stone', a name no 
doubt given to it on account of its great hardness (it is next to 
the diamond on Moh's scale). Marcasite apparently come from 

Greece 1 5 

mar hast, which probably means 'pyrites'. It is thrilling also to 
find a mineral called kibaltu, though whether there is a con- 
nexion between this and cobalt remains for the present 

The metal mines in the Taurus mountains were being actively 
worked by Babylonian firms as early as 2300 B.C. Their 
representatives and agents, mostly Assyrian, had business 
offices, and their safes were filled with business letters, receipts, 
cheques, and so on. At Kara Eyuk in Cappadocia two interest- 
ing tablets relating to the metal industry have been excavated. 
The first reads roughly as follows: 'Labikum writes as follows: 
Askutum and Kurub-Istar say to Ana-Nada: Ana-Samsi has 
brought 2 talents 10 manehs and 4 shekels of lead with your 
seal. We have packed the lead and have paid 2| manehs of raw 
metal and \ maneh 6 shekels of pure metal to the house of the 
Garum. The rest of the lead 2 talents 6| manehs and 4 shekels 
we have reserved, and we send you silver in payment. In 
accordance with your order, Ana-Samsi has brought down the 
whole to you.' The second tablet states that 4^ shekels of iron 
of the best quality had been dispatched to a customer. 

The Semitic word for iron, barzelin Hebrew, parzel in Baby- 
lonian, parzillu or barzillu in Assyrian, is written in the second of 
the above tablets in Sumerian characters KU-AN, meaning 'metal 
of the god' or 'metal of heaven'. The Sumerian name thus corre- 
sponds to the Semitic barzi-iliand Egyptian ba-en-pet (p. 4). It 
therefore seems likely that the Egyptians derived their name for 
iron, and consequently the metal itself, from Asia Minor, as has 
already been mentioned. Incidentally, Professor Sayce suggests 
that the linguistic evidence just described may perhaps solve 
the mystery of the Old Testament Terizzites', who would seem 

to have been 'the metal-workers'. 


4. Greece 

WITH two exceptions that are, however, of the first con- 
sequence classical antiquity in Greece has little direct interest 

1 6 Greece 

for the historian of chemistry. Accomplished as the ancient 
Greek craftsmen were, they showed small originality in technical 
procedure, and it is to the philosophers that we must turn for the 
two theories that proved of paramount importance in the 
development of chemical thought and practice. The first of 
them, in its mature form, was due to Aristotle, and the second 
was the composite contribution of the Atomists. It will be con- 
venient to deal with each of them in turn. 

Aristotle (384-322 B.C.), the tutor and friend of Alexander the 
Great, and the most celebrated scientific authority of antiquity, 
appears to have been one of the first to insist upon an experi- 
mental and observational basis for a knowledge of nature. The 
exaggerated reverence, however, with which he came to be 
regarded in the Middle Ages, and his semi-official recognition as 
the orthodox philosopher of both Islam and early Christianity, 
caused much of his true spirit to be obscured; with the result 
that a false Aristotelianism proved to be a millstone round the 
ineck of chemistry until long after the Renaissance. Aristotle's 
theory of the constitution of matter is to be found mainly in the 
De Caelo, Books III and IV, in the De generations et corruptions, 
and in the Meteor ologica. He supposed that the basis of the 
material world was a primitive matter or prima materia, which 
had, however, only a potential existence until impressed with 
form. Form is that which gives to every body its individuality. 
In its simplest manifestation it gives rise to the 'Four Elements', 
Fire, Air, Water and Earth, which are distinguished from one 
another by their qualities. The four primary qualities are the 
fluid, the dry, the hot, and the cold, and each element possesses 
two of them. Hot and cold, however, and fluid and dry, are 
contraries and cannot be coupled; hence the four possible 
combinations of them in pairs are : 

Hot and dry, assigned to Fire. 
Hot and fluid, assigned to Air. 
Cold and fluid, assigned to Water. 
Cold and dry, assigned to Earth. 

Greece 17 

In each element, one quality predominates over the other: in 
earth, dryness; in water, cold; in air, fluidity; and in fire, heat. 
None of the four elements is unchangeable ; they may pass into 
one another through the medium of that quality which they 
possess in common; thus 
fire can pass into air through 
the medium of heat, air into 
water through the medium 
of fluidity, and so on. Two 
elements taken together 
may pass into a third by 
each parting with one 
quality, subject to the limi- 
tation that this process must 
not leave two identical or 
contrary qualities ; thus fire 
and water, by dropping the 
dry and cold qualities, could 
produce air, or by dropping 
the hot and fluid qualities 
could give rise to earth. In 
all these changes it is only 
the form that alters; the 
matter of which the ele- 
ments are made never 
changes, however diverse 
and manifold the changes Fig. 7. ARISTOTLE 

of form may be. 

All other substances are composed of all the elements or 
'simple' bodies. 

For they all contain Earth because e^ery * simple body* is to be 
found specially and most abundantly in its own place. And they 
all contain Water because (a) the compound must possess a 
definite outline and Water, alone of the 'simple' bodies, is readily 
adaptable in shape : moreover (b) Earth has no power of cohesion 
without the moist. On the contrary, the moist is what holds it 

2613-4 C 

1 8 Greece 

together; for it would fall to pieces if the moist were eliminated 
from it completely. They contain Earth and Water, then, for the 
reasons we have given: and they contain Air and Fire, because 
these are contrary to Earth and Water (Earth being contrary to Air 
and Water to Fire, in so far as one Substance can be 'contrary' to 
another). Now all compounds presuppose in their coming-to-be 
constituents which are contrary to one another: and in all com- 
pounds there is contained one set of the contrasted extremes, i.e. 
cold-dry (Earth) and cold-fluid (Water). Hence the other set [i.e. 
hot-fluid (Air) and hot-dry (Fire)] must be contained in them also, 
so that every compound will include all the 'simple' bodies. 

It is not altogether easy to follow this argument, in which 
Aristotle seeks to prove that Fire, Air, Water and liarth must 
each and all necessarily be contained in every other substance. 
A little reflection, will, however, enable us to understand its 
chief points. Aristotle maintained that each element had a 
natural tendency to move to 'its own place'. Conceiving the 
universe as a structure of some fifty-nine concentric spheres, he 
made earth occupy the innermost, water the next, and air and 
fire the third and fourth, though there was no definite line of 
demarcation between them, particularly in the case of the last 
pair. Since the 'proper place' for Earth is the (planet) Earth, 
it follows that all terrestrial substances must, of all the four 
elements, contain Earth at least. Secondly, they must all 
contain Water, for the two reasons he mentions reasons which 
may not satisfy us but are perfectly intelligible. The real 
difficulty then arises : what does Aristotle mean by saying that 
since all compound substances contain Earth and Water they 
must therefore contain Fire and Air as well ? We can begin to 
get an answer to this question by referring to a passage which 
occurs a little earlier than, that quoted. 'There are differences in 
degree in hot and cold. Although, therefore, when either is 
fully real without qualification, the other will exist potentially; 
yet when neither exists in the full completeness of its being . . . 
both by combining destroy one another's excesses, so that there 
exist instead a hot which (for a "hot") is cold and a cold which 

Greece 19 

(for a "cold") is hot.' This seems to imply that a compound of 
Earth and Water only would show the qualities of these elements 
in an excessive or absolute degree, which is contrary to observa- 
tion. The contraries are required to modify this character of 
excess and so to explain the actually observed properties of 
terrestrial substances. 

The proportion in which the various elements occur in 
different substances is infinitely variable ; hence the existence of 
such an enormous number of distinct compounds. But since 
each element can, as we have seen, be transformed into any 
other, it follows that any compound can likewise be transformed 
into any other by some device that will alter the relative pro- 
portions between the elements of which it is composed. Here 
we have the germ of all theories of metallic transmutation. If 
lead and gold both consist merely of fire, air, water and earth, 
all of which are interconvertible, why may the dull and common 
metal not be transmuted into the shining, precious one ? Such 
was the question with which generation after generation of 
alchemists confounded the sceptics and justified their ceaseless 
search for the philosopher's stone. 

On the more detailed problem of the formation of metals and 
minerals as such, Aristotle expresses his views at the end of the 
third book of the Meteor ologica. He maintains here that there 
are two 'exhalations', one vaporous and the other smoky; the 
former is produced when the sun's rays fall upon water, and is 
moist and cold, while the smoky exhalation is formed when the 
rays fall upon dry land, and is hot and dry. Each exhalation is, 
however, mixed with more or less of the other. To the two 
exhalations correspond two classes of bodies that originate in 
the earth, namely, minerals and metals. The heat of the dry 
exhalation is the cause of all minerals, i.e. these substances are 
composed mainly of the * smoky' exhalation. Such are the kinds 
of stones that cannot be melted, and realgar, ochre, ruddle, 
sulphur and other substances of that kind. The 'vaporous' 
exhalation is the cause of all metals, those bodies which are 
either fusible or malleable, such as iron, copper, gold. All these 


2O Greece 

originate from the imprisonment of the vaporous exhalation in 
the earth, the dryness of which compresses it and finally con- 
verts it to metal. Thus, since neither exhalation is entirely free 
from the other, metals and minerals, like all other substances, 
are composed of each of the four elements, but in metals the 
predominating elements are water and air (chiefly water), while 
in minerals they are earth and fire (chiefly earth). 

We shall find in the sequel that in this theory of metallic 
constitution we have the seed of the celebrated or perhaps 
notorious Theory of Phlogiston, which can be traced step by 
step from Aristotle to its final development at the hands of 
Becher and Stahl in the seventeenth and eighteenth centuries. 

A striking testimony to Aristotle's scientific acumen is that he 
seems to have distinguished very clearly between mechanical 
mixture and chemical combination. In strict Aristotelian 
terminology, the former is called avvOeais and the latter fut?, 
the most common and conspicuous type of combination, viz. 
that between liquids, being distinguished by the special term 
xpacris. Professor Joachim interprets Aristotle's ideas as follows : T 

If two or more bodies are put together without alteration, this is 
a avv6cris and the resultant is a mechanical mixture. Suppose that 
we first chop up the component bodies into particles too small for 
the normal eyesight to discriminate them, and then shuffle them 
together: we should still have a mere mechanical mixture, 
although relatively to our vision the result would seem to be 
a chemical compound. It would not really be a /u^fleV [chemical 
compound] : for the component particles still retain their distinctive 
natures. They form an aggregate, not a, genuine unity. If we 
symbolize the components as A B C D, the resultant is A -f B -f- C -f D. 
If we divide it far enough, we shall reach parts which are A or B 
or C or Z), and not (A+B + C+D): i.e. the smallest parts of the 
whole are different in character from the whole. 

But now suppose that A, B, C and Z>, by acting and reacting on 

one another, produce an alteration in one another's qualities. 

Suppose further that this reciprocal alteration continues until 

a resultant, x, emerges, whose qualities are modifications of the 

1 Journal of Philology, xxix. 72-6 (1903). 

The Classical Atomic Theory 21 

qualities of the components, and yet are different from the 
qualities of any (and of all) of them. Suppose further that every 
part of x, however far you subdivide it, retains the character of the 
whole. And suppose finally that (by appropriate processes of re- 
solution) you can recover (or re-create) from x components the 
same in character as the original A, B, C and D. If these condi- 
tions are fulfilled, x is a yuyftiv or KpaOev [compound], emerging 
from the ju,tf is or Kpdcris of the {JLLKTCL [components] A, B, C and D 
... A [Liyjdiv is such that (i) its components have really merged 
into a unity, instead of forming a mere aggregate by juxtaposition: 
and that (2) the components, although contained in the resultant, 
are contained there in an altered form. ... It is thus clear that 
Aristotle recognizes in principle the modern distinction between 
mechanical mixture and chemical combination. But the details of 
his theory of combination are quite remote from modern specula- 

5. The Classical Atomic Theory 

PERHAPS the greatest legacy bequeathed to chemists by the 
philosophers of Greece though its value was not fully realized 
till after the lapse of two thousand years was the theory that 
matter is composed of atoms. Our detailed knowledge of this 
theory is derived almost entirely from the poem of Lucretius 
(first century B.C.) called De Rerum Natura, in which the earlier 
views of Leucippus and Democritus (fifth century B.C.) and 
Epicurus (about 300 B.C.) are logically marshalled and brilliantly 
expounded. The chief points of permanent value, in the light of 
subsequent developments, are as follow: 

1 . There is only one ultimate species of matter. 

2. Matter is indestructible and cannot be created. 

3. Matter is not continuous, but discrete, i.e. it has a 'grained" 


4. Matter is composed of 'atoms' which are invisible, physically 

indivisible, indestructible, eternal, and impenetrable. 

5. Between atoms there is simply a void empty space. 

6. The atoms of different substances are different in shape, size, and 


22 The Classical Atomic Theory 

7. Atoms are in constant motion rectilinear according to Demo- 

critus colliding with, and rebounding from, one another 
'like motes in a sunbeam". 

8. Substances differ in properties according to the nature , number 

and arrangement of the atoms of which they are composed. 

This arbitrary selection of certain features must not be 
allowed to give an entirely erroneous impression of the Greek 
atomic theory. As with Aristotle and the idea of chemical 
combination, so with the atomists and their theory : superficially 
their conceptions were very similar to those which we owe to 
Newton, Dalton and others, but in wider ramifications the 
divergence is great. There is also a more basic difference 
between the ancient and modern theories. While it would be 
incorrect to say that the ancient theory was not based upon 
observational facts, it is nevertheless true that the number and 
quality of these facts were ridiculously inadequate to the grand 
scheme erected upon them; whereas the modern theory is 
supported by countless thousands of well-established, relevant 
facts. Had their theory been based upon, or verified by, ex- 
perimental observations, the Greeks might have made incalcu- 
lable advance in chemistry ; actually, however, it was no more 
than a shrewd and lucky guess (or, if you will, a flash of insight), 
and its importance lies in the influence it exerted upon later 
thinkers until it finally suffered a drastic metamorphosis into the 
atomic theory of John Dalton at the beginning of the nineteenth 

It is fatally easy to read into the views of bygone scientists 
ideas of a later period, and to credit them with discoveries or 
theories or opinions to which, in actual fact, they have no claim 
whatever. The superficial resemblance between the classical 
and modern atomic theories very largely vanishes in the light of 
closer inspection. The classical theory was, indeed, meta- 
physical rather than physical, and its features become grotesque 
when carefully examined. Lucretius, for instance, assumes that 
the atoms slightly deviate from a rectilinear path for no other 

The Classical Atomic Theory 23 

reason than that he may thereby deduce a theory of free-will! 
The service which the Greek atomists rendered to chemistry 
was that they familiarized men with the conceptions of atoms 
and empty space ; conceptions that remained latent for centuries 
afterwards but ultimately 
lent themselves to a sys- 
tematic and scientific treat- 

The wonderful achieve- 
ments of Hellenic thinkers 
so dazzle our intellectual 
vision that we are apt to re- 
gard them as the possessors 
of a scientific and rationa- 
list attitude that was really 
quite foreign to them, or at 
least to most of them. Greek 
interpretations of Nature 
are saturated with supersti- 
tion , mythology, astrological 
beliefs and even magic. 
For Aristotle, the stars were 
deities ; Empedocles be- 
lieved himself capable of 
magic powers ; Plato considered the world to have a soul and, in 
his Timaeus, plainly shows his belief in occultism ; he also speaks 
of the stars as ' divine animals' ; and Pythagoras, or his followers, 
ascribed mystic powers to numbers. While, therefore, the 
Greeks must be given full credit for having presented science 
with many conceptions that proved invaluable in later times, 
we should be doing less than justicp to the great men who 
followed if we imagined them merely to have revived Hellenic 
knowledge. In the form in which Lucretius left it, the atomic 
theory could never have occasioned the wonderful progress of 
chemistry witnessed by the nineteenth century: that progress 
was rendered possible by the genius of John Dalton, whose 


24 China 

atomic theory, though a direct descendant of that of Lucretius, 
bears the same sort of relation to it as a man does to one of his 
simian ancestors. 

6. China 

THE inhabitants of China, with their air of inscrutable wisdom, 
have always appeared to the eyes of Western beholders as the 
possessors of ancient and mysterioiis lore. In consequence, they 
have frequently been credited with the first discovery or in- 
vention of many objects, arts and crafts the early history of 
which is obscure. Oxygen, gunpowder, china-ware and print- 
ing are among the discoveries attributed to the Celestial Empire : 
perhaps with reason and perhaps baselessly. The principal 
difficulty with which the investigator is faced is the fact that in 
many cases it is quite impossible to date the authorities, while 
even those whose period is approximately known are often inter- 
polated with such skill that criticism is at a loss to distinguish the 
original from the added. Until historians have succeeded in 
reducing to order this heterogeneous mass of historical and 
pseudo-historical records, very little trustworthy knowledge of 
Chinese chemistry will be available. 

Dr. O. S. Johnson has recently suggested that alchemy was an 
indigenous product of China, and that it arose from the philo- 
sophy of Tao-ism. According to this philosophy, the entire 
universe was identical in substance and was animated and 
dominated by a cosmic soul, manifesting itself in the dual forces 
of Yin and Yang. All minerals or metals were thus substantially 
the same, but differed in qualities in proportion to their relative 
infusion with Yin and Yang. Base metals might therefore be 
transmuted into precious metals by the dual method of elimi- 
nating the more material Yin qualities in their composition, and 
by augmenting, or refining, the more spiritual Yang qualities. 
The first instance recorded in Chinese history of attempts to 
transmute metals by artificial means, says Johnson, we find 
during the reign of the famous emperor Wu Ti (140-86 B.C.), 
but the principal authority on alchemy in China is Ko Hung, of 
the fourth century of our era. He was a devoted Taoist, and 

China 25 

under the pseudonym Pao Pu Tzu ('Old Sober-sides') he wrote 
in A.D. 330 an important treatise on Taoist philosophy and 
alchemy. It is divided into two parts, of which the first, called 
Nuy peen or 'inner chapters', consists of twenty chapters on the 
transmutation of the metals, elixirs of life, ascetic rules for 
prolonging life, and methods of attaining immortality. The 
account of making yellow and white elixirs for converting base 
metals into gold and silver respectively is chiefly contained in 
chapters 4, n and 16. Ko Hung states that a man may prolong 
his life by taking medicines made from plants, but can only 
become immortal by the use of a Divine Elixir made from 
minerals and metals. It is difficult to identify the substances 
that were to be employed in the preparation of this elixir, but 
red and yellow arsenic sulphides, sulphur, cinnabar, alum, salt, 
white arsenic, oyster shells, mica, chalk and the resin of the pine 
tree were certainly included among them. The resulting elixir, 
when thrown on to mercury, or a mixture of lead and tin con- 
tained in an iron pot, converted the metal into gold or silver, 
while taken as a medicine for 100 days it made a man immortal. 

That the Chinese discovered for themselves many properties 
of minerals, and that they attempted to prepare medicines 
which should confer long life or immortality, is not to be 
doubted; but the greatest living historian of chemistry, E. O. 
von Lippmann, believes that alchemy proper reached China 
from the West in the course of the eighth century A.D., after the 
port of Kanton had been opened to foreigners. In A.D. 714 the 
first Arab ships dropped anchor at Kanton, and thereafter trade 
developed with amazing rapidity. The eminent sinologist 
Richthofen reached the conclusion that only from that time and 
source did the Chinese acquire a true alchemy, and that sub- 
sequently they described it as their own national discovery. 
To support the claim they forged' all documents that they 
considered necessary, either writing whole books and ascribing 
a completely false antiquity to them, or cleverly interlarding 
genuine works with spurious passages. 

Amid these conflicting views and claims it is not possible to 

2b India 

arrive at any firm judgement, but there certainly is a close 
similarity between Chinese alchemy and that of Islam (see 
p. 46), so that it at least seems certain- that the two were derived 
either from a common source or one from the other. 

7. India 

THE Indians are the blood-relations of the European peoples, 
and it would be extremely surprising if so ancient a civilization 


as that of India had failed to produce chemical facts and theories : 
though we should remember that Egyptian chemistry was 
'almost completely devoid of serious speculation. Unfortunately, 
we know with certainty but little of the history of chemistry in 
India, though there is a large medieval literature, in Sanskrit, 
in which chemical and medical facts are described. The difficul- 
ties of investigation are the same as those encountered in the 
case of China, viz. the great uncertainty in the dating of 

Rome 27 

authorities, and the impossibility of accurately distinguishing 
between indigenous and imported knowledge. 

It has been suggested that Greek natural philosophy was 
largely derived from that of ancient India : and as steadfastly 
denied. There is certainly truth in the statement that an early 
Indian philosopher named Kanada probably prior to Leu- 
cippus supposed matter to be composed of five elements 
(earth, water, light, air and 'ether') which were themselves made 
up of indestructible and eternal atoms. Possibly this theory 
found its way to Greece, though there is no satisfactory evidence 
of the fact. In any case, it was the Greek, and definitely not the 
Indian, form of the theory that influenced the Western world, 
so that in this book we may perhaps leave the matter there. 

The question of Indian influence arises again during the 
period of Islamic chemistry. Certain Indian chemists, such as 
Biwan the Brahman, are occasionally quoted by Muslim authors, 
but the balance of evidence goes to show that chemistry was 
carried to India by the Muslims rather than to Arabia by the 
Indians. Yet it is only proper to repeat the statement that the 
history of Indian chemistry and its relation to the outer world 
has yet to be written. 

8. Rome 

IMPERIAL Rome has left us no grand chemical generalizations or 
striking chemical discoveries. An eminently practical people, 
the Romans were quick to perceive the value of applied science, 
and Roman artificers and engineers were unequalled in skill and 
ingenuity. The whole of the ancient world experienced their 
activity: whether one goes to Constantinople or Frejus, to 
Algeria or Spain, or to the nearer Mendips, the traces of the 
Roman are obvious. Mining and metallurgy, the quarrying of 
stone, dyeing, painting, wine-making all imply more or less 
chemical knowledge, and the facts described in Pliny's Natural 
History 1 and in the medical works of Galen clearly demonstrate 
:he vast body of empirical science at the disposal of the Empire. 

1 See Dr. Kenneth Bailey's The Elder Pliny 1 s Chapters on Chemical 
Subjects t London, 1929. , 

28 Rome 

Yet when the historian of chemistry attempts to lay his finger 
on definite advances that the Romans made he finds it an 
almost impossible task. Perhaps here and there a recipe is given 


that cannot be paralleled in an earlier age ; here and there is 
a process that seems particularly appropriate to special cir- 
cumstances ; here and there a new experiment is described ; but 
1 hat is all. Roman craftsmen for the most part merely applied 
>ld knowledge with new efficiency, and Roman thinkers were 

The Leyden and Stockholm Papyri 29 

more attracted to law than to the philosophy of nature. So it is 
that we must turn to the later developments of Greek thought, 
in the city of Alexandria, if we wish to assist at the christening 
of the infant chemistry. 

9. The Leyden and Stockholm Papyri 

THE Egyptian metallurgists and other technical workers doubt- 
less worked out very frequently recipes that they considered 
worth recording. At the same time, the fact that such informa- 
tion was extremely valuable must have made them reluctant to 
write the recipes in so clear a manner that, in cases of theft, the 
thief would be able to understand and profit by them. More 
probably they would resort to a semi-cryptic language, a custom 
not unknown even to modern workers- in similar circumstances. 
Unluckily, very few Egyptian technical manuscripts have sur- 
vived, a misfortune which may be accounted for in part by an 
act of the Emperor Diocletian in A.D. 290 or thereabouts. It 
seems probable that, in the course of their work, the ancient 
metal-workers had occasionally prepared alloys more or less 
closely resembling the precious metals gold and silver. Too 
shrewd and accomplished to deceive themselves very often, they 
yet may have succumbed to the temptation of deceiving others 
of less experience, passing off a good imitation of gold as the 
genuine metal and thus acquiring an easy though dishonest 
wealth. It can readily be imagined that such a delightfully 
simple way of solving financial difficulty would rapidly become 
popular, and that counterfeiters found a credulous market for 
their spurious wares. Historians tell us that this actually 
happened, and the nuisance at length became extremely serious. 
Diocletian is therefore said to have commanded a diligent 
inquiry to be made 'for all the ancient books which treated of 
the admirable art of making gold and silver, and without pity 
committed them to the flames ; apprehensive, as we are assured, 
lest the opulence of the Egyptians should inspire them with 
confidence to rebel against the Roman Empire'. But, as Gibbon 
(who relates the story) sagely remarks, 'If Diocletian had been 

30 The Leyden and Stockholm Papyri 

convinced of the reality of that valuable art, far from ex- 
tinguishing the memory, he would have converted the operation 
of it to the benefit of the public revenue. It is much more likely 
that his good sense discovered to him the folly of such magni- 
ficent pretensions, and that he was desirous of preserving the 
reason and fortunes of his subjects from the mischievous pursuit/ 

Fortunately, two manuscripts escaped the general massacre. 
They appear to be the recipe-books of an Egyptian chemist, of 
about the time of Diocletian, and were discovered in a tomb at 
Thebes in the early years of the nineteenth century. One of 
them is preserved at Leyden, and is therefore generally known 
as the Leyden papyrus, while the other, the Stockholm papyrus, 
belongs now to the Victoria Museum at Upsala. The Leyden 
papyrus was translated and analysed by Berthelot, while in 1913 
Lagercrantz translated the Stockholm papyrus and provided it 
with a critical commentary. Although both manuscripts date 
from the third century of our era, much of the material in them 
is undoubtedly far more ancient and goes back to the days when 
metallurgy was a secret craft controlled by the Egyptian priest- 

The Leyden papyrus deals mainly with metals, and though 
some of its recipes are plainly expressed, others are more 
:ryptically worded and give mere hints or suggestion as to the 
processes they describe. Of particular interest is the fact that 
tfhile many of the recipes deal with the falsification and * pro- 
duction' of the precious metals, they are noticeably free from 
superstitious and magical theories. Similar remarks apply to the 
Stockholm papyrus, which treats mainly of methods of 'pre- 
paring' the precious stones, that is, of manufacturing passable 
imitations. of them from glass and other materials. There seems, 
indeed, little doubt that until the Alexandrian School began to 
make its philosophical and mystical influence felt, the technical 
workers were almost entirely free from the speculative im- 
pulse, and carried on their activities in a purely empirical way 
and with a mere utilitarian and practical aim. In the absence of 
reliable criteria, they may occasionally have been mistaken as to 

if, xi. OF THE 

32 The School of Alexandria 

the real nature of the metallic alloys they prepared, but it is 
more likely that instructions for the 'doubling' of gold were 
rarely misinterpreted by the chemist for whom they were 
intended. He, at least, would know that 'artificial gold' was but 
a technical term, and the Ley den and Stockholm papyri convey 
the impression that their writer was too intelligent a man, and 
too expert a craftsman, to believe in the actual transmutation of 
metals or in the genuineness of the 'precious stones' prepared in 
the laboratory. 

10. The School of Alexandria 

ALEXANDRIA, founded in 332 B.C. by Alexander the Great, 
rapidly grew to be the greatest and most important town of 
the ancient world. Under succeeding sovereigns, particularly 
Ptolemy Soter (323-285), Ptolemy Philadelphus (285-247) and 
Ptolemy Kuergetes (247-222) an enormous library was gathered 
together Philadelphus even being fortunate enough to buy 
Aristotle's library and a museum or university was built to 
house the brilliant scholars attracted thither from various parts 
of Greece. A mathematical school was founded by the great 
Euclid himself, and among its celebrated pupils were Archi- 
medes, Hipparchus, Eratosthenes, and Apollonius of Perga. 
Grammar, literary criticism, philology, astronomy and medicine 
all found learned teachers and enthusiastic disciples, and the 
commercial industry of Alexandria was paralleled only by its 
intellectual activity. 

In the history of chemistry, Alexandria played a part of 
fundamental importance. Here, for the first time, Egyptian 
practical arts and Greek scientific thought were brought into 
effective contact ; but the result was not, as perhaps one would 
expect it to have been, the immediate synthesis of a logical 
system of chemistry. Chemistry indeed may be said to have 
begun in Alexandria, but it was almost stifled at birth through 
the influence of two philosophical developments, some know- 
ledge of which is essential to a proper understanding of the pro- 
gress of the science. They are Gnosticism and Neo-Platonism. 


ii. Gnosticism 

THE first philosophico-religious system that profoundly in- 
fluenced the childhood of chemistry is that known as Gnosti- 
cism. Arising in the early years of the Christian era, it appears 
in its full strength about A.D. 120 as a singular mixture of the 
most diverse elements. Some parts of it derive from Greek 
philosophy, others from Christianity, and still others from 
a Persianized form of the old Babylonian religion. Such a com- 
posite structure was inevitably confused, and the confusion was 
rendered worse by the marked predilection for symbolic expres- 
sion shown by the principal Gnostics. Yet Basilides, Valentine, 
Marcion and the other exponents of the system had one thing in 
common : their belief that they possessed the secret of a sublime 
knowledge or gnosis which had been transmitted to them by 
ineffable and occult means. This transcendental knowledge had 
nothing in common with our science. 'We passionately seek the 
truth/ says de Faye, 'that is, the real, whether in the past or in 
the phenomena immediately before us. We desire to know that 
which is. The Gnostics cared very little for the phenomena of 
the sensible world ; the physical explanation of the Cosmos had 
no interest whatever for them.' They were much more anxious 
to know the invisible world, which they imagined to be peopled 
with abstract yet living entities, and of which they described 
their ideas in the strange and mysterious language of an in- 
volved symbolism. It is significant that one of the earliest 
chemical writers, Zosimos, was a Gnostic. 

12. Neo-Platonism 

NEO-PLATONISM has been described as the last great creation 
of Greek philosophy and the noblest product of latter-day 
paganism. Essentially it was a logical development of the 
Platonic philosophy, combined, however, with ideas taken over 
from the Stoics and Aristotle. Its principal creator was the 
Egyptian Plotinus (c. 204-270), whose conceptions were ex- 
tended and modified by Porphyry (233-304?), lamblichus (died 
about 330), and others. The world to a Neo-Platonist was 
2613-4 D 

34 The Fusion of Practice with Speculation 

imbued throughout with a soul, in which even inanimate 
objects shared. The ordinary facts of nature, which we account 
of paramount importance as the basis of natural science, were 
regarded as plastic and variable manifestations of a transcen- 
dental spiritual world, and were consequently neglected. More 
essential to the Neo-Platonist than the external properties of 
substances were their occult or sympathetic properties, by which 
they could act upon one another even at a distance. All material 
bodies were, like all spiritual entities, in harmony and sympathy 
with one another, but matter was the principle of unreality or 
evil and the disciple therefore attempted to detach himself from 
the things of sense. The universe in part expressed itself through 
the figures formed by the movements of the sun, moon, planets 
and stars, and the celestial bodies both exerted an influence and 
were signs of the future. Magic, as then practised by the Gnostics, 
Plotinus denounced, but rather because its contemporary form 
was, in his opinion, corrupt than because it was altogether base- 
less. Numbers had mystical powers, and divination was a reason- 
able art. 

Such are the points of Neo-Platonism that immediately 
concern us. Put thus baldly, they convey an unworthy idea of 
the sublimity of the great system of philosophy in which many 
profound thinkers have seen the highest expression of meta- 
physical thought; but it was just this detachment from the 
material world, and belief in the occult properties of the con- 
tents of the universe, that largely defined the course of chemical 
theory in its early days. Sympathetic action, action at a distance, 
the distinction between occult and manifest properties, the 
influence of the stars, the mystical powers of numbers, are all 
ideas which permeate chemistry from its beginnings at the time 
of Plotinus until the close of the seventeenth century. 

13. The Fusion of Practice with Speculation 

THE intercourse between Egyptian artificers and the followers 
of Neo-Platonism and Gnosticism appears to have led the latter 
to apply their mystical theories to the supposed art of gold- 

Zosimos the Panopolitan 35 

making and the nature and generation of metals and minerals. 
Accepting transmutation as a fact, these primitive chemical 
philosophers erected amazing structures of fanciful hypothesis 
to account for it, discoursed at length upon the explanation of 
the changes involved and, to lend dignity to the new science, 
maintained that it was of great antiquity and that the god 
Hermes or Thoth himself was its founder. When the knowledge 
of the hieroglyphic characters was lost, they were claimed by the 
chemists as expositions of chemeia, the Art of the Black Land, 
Egypt or Khem, and the fabulous treasures of the Pharaohs were 
stated to have been amassed through successful transmutations. 
|The name chemeia appears for the first time in the writings 
Attributed to Zosimos the Panopolitan, whose life and works we 
must now consider. 

14. Zosimos the Panopolitan 

ZOSIMOS of Panopolis, in Upper Egypt, is the most ancient 
alchemical author of whom we have genuine writings and whom 
we can identify. A contemporary of Plotinus and Porphyry, he 
lived towards the end of the third century A.D. or possibly at the 
beginning of the fourth, and spent his early youth in Alexandria, 
where he studied and wrote. Suidas, who flourished about the 
year A.D. 1000, tells us that Zosimos composed an encyclopaedic 
work on chemistry in at least twenty-eight books, which he dedi- 
cated to his ' mystical sister' in the Art, Theosebeia. A few 
treatises attributed to him are still in existence, and have been 
published and translated by Berthelot; among them are his 
Authentic Memoirs, A Treatise on the Alembic with Three Beaks, 
On the Evaporation of the Divine Water that fixes Mercury, The 
Book of Virtue: On the Composition of Waters, and a Treatise on 
Instruments and Furnaces. These may be partly or mainly 
genuine, but probably all contain interpolations of a later date. 
They coffer us the most bizarre picture of Gnostic theory inter- 
mingled with chemical fact, ecstatic visions, descriptions of 
apparatus, and injunctions to the reader to keep the secret of 
the Art from the vulgar. 

D 2 

36 Zosimos the Panopolitan 

Zosimos tells us that the chemical arts were practised in Egypt 
under royal and priestly control, and that it was illegal to publish 
any work on the subject. Only 'Democritus' had dared to in- 
fringe this regulation; as for the priests themselves, they had 
engraved their secrets on the walls of the temples in hiero- 
glyphic characters, so that even if any evilly disposed people 
had ventured to brave the darkness of the sanctuaries they would 
have found the inscriptions unintelligible. The Jews, however, 
had been initiated into the mysteries and afterwards trans- 
mitted them to others. 

Believing in the possibility of metallic transmutation, Zosimos 
describes the theory or rather theories of the process in 
symbolic and mystical language of which the following is a 
typical example: 1 

I fell asleep and saw before me a priest standing upright before 
a dome-shaped altar, leading up to which were fifteen steps. The 
priest remained standing, and I heard a voice from on high which 
said to me: 'I have accomplished the action of descending the 
fifteen steps walking toward the darkness, and the action of 
ascending the steps going towards the light. The sacrifice renews 
me, rejecting the dense nature of the body. Thus necessarily con- 
secrated, I become a spirit/ Having heard the voice of him who 
stood upright upon the dome-shaped altar, I asked him who he 
was. In a weak voice he answered me in these terms: 'I am Ion, 
priest of the sanctuaries, and I suffer intolerable violence. Some 
one came quickly in the morning, cleaving me with a sword, and 
dismembering me according to the rules of the combination. He 
removed all the skin from my head with the sword which he held ; 
he mixed my bones with my flesh and burned them with the fire 
of the treatment. It is thus, by the transformation of the body, 
that I have learned to become spirit. . . .' 

It is difficult to decide whether language of this kind is in- 
tended to portray in symbolic form definite chemical operations, 
or whether it merely represents a hypothetical philosophy of 
certain chemical changes or whether, indeed, it has any mean- 
ing at all. We can, however, in certain passages, discern a more 
1 Stillman, The Story of Early Chemistry, London, 1924, p. 163. 

Zosimos the Panopolitan 37 

prosaic level whence we may extract relics of Zosimos's un- 
deniably wide knowledge of practical chemistry. Thus he 
mentions the preparation of mercury from cinnabar, and dis- 
cusses the question whether or not mercury should be called 
a metal (deciding that it is 'a metal and no metal', a 'neutral' 


substance or a 'hermaphrodite'). The 'second mercury', arsenic, 
he says can be obtained from sandarach [arsenic sulphide], by 
first roasting it to get rid of the sulphur, when the 'Cloud of 
Arsenic' [arsenious oxide] will be left. If this is heated with 
various [reducing] substances, it yields the second mercury 
[metallic arsenic], known as the 'Bird', which can be used to 
convert copper into silver [copper arsenide is a white metallic- 
looking compound not altogether unlike silver]. White lead may 
be obtained by exposing lead to 'vapours' [scil. of acetic acid, 
vinegar] ; on heating it yields litharge. If litharge is combined 
with vinegar, the product [sugar of lead, lead acetate] has the 

38 Zosimos the Panopolitan 

remarkable property of being both sweet and salt-like ; on keep- 
ing it is transformed into white lead [by the action of atmo- 
spheric carbon dioxide, &c.]. Other chemicals mentioned are 
realgar, ochre, haematite, natron, and chalkanthos [Fe 2 O 3 ]. 

Chemical apparatus may consist of pottery or glass, the latter 
being particularly convenient on account of its transparency and 
impermeability to certain vapours such as that of mercury. The 
best glass vessels, Zosimos assures us, come from Askalon in 
Syria, an observation of peculiar interest in that a Cairene 
chemist of the fourteenth century also makes special mention of 
the Askalon vessels. For fixing parts of apparatus together, clay, 
fat, wax, gypsum and similar substances may be used. Heat may 
be applied by (a) the sun, (b) fermenting manures, (r) sand-baths 
or baths of hot ashes, (d) water-baths and (e) furnaces. 

Facts and descriptions such as these show quite clearly that 
Zosimos had a by no means negligible laboratory experience, 
and that he and his like are not to be lightly dismissed as mere 
theorizers. Yet they were obsessed with mystical and super- 
stitious philosophies current at the time, and appear to have 
welcomed the fabulous as much as the true, if not more. We 
inevitably find it difficult to understand how a man as well 
versed in simple metallurgical and chemical facts as Zosimos 
must have been, could accept the following account of the 
origin of tin : l 

In a place in the far west, where tin is found, there is a spring 
which rises from the earth and gives rise to it like water. When the 
inhabitants of this region see that it is about to spread beyond its 
source, they select a young girl remarkable for her beauty and place 
her entirely nude below it, in a hollow of the ground, in order that 
it shall be enamoured of the beauty of the young girl. It springs at 
her with a bound, seeking to seize her; but she escapes by running 
rapidly while the young men keep near her holding axes in their 
hands. As soon as they see it approach the girl, they strike and cut 
it, and it comes of itself into the hollow and of itself solidifies and 
hardens. They cut it into bars and use it. 

1 Stillman, op. cit., p. 168. 

A Retrospect 39 

Yet such descriptions, whether intended to be taken literally 
or as merely symbolical, grow more and more frequent and more 
and more incomprehensible as we pass to those chemists who 
succeeded Zosimos: Pelagius, Synesius, Heliodorus, Olympi- 
odorus and others. Speculation and occult theory grow ever 
wider apart from experimental fact, and at length we encounter 
the conception of a philosopher's stone, a divine elixir, which, 
if projected upon 'base' metals in fusion, will convert them into 
gold 'better than that of the mines'. When this remarkable idea 
was first evolved we have no definite knowledge, but from the 
seventh century till the seventeenth it was the object of un- 
ceasing search on the part of the great majority of chemists, and 
indeed formed the central theme of chemistry for the major 
portion of its existence. 

15. A Retrospect 

EARLY chemistry is somewhat difficult to follow, and we shall 
probably find it useful to clear our ideas by taking a bird's- 
eye view of the territory we have already traversed, before 
entering upon the travels in Arabia that await us. We have 
seen that technical arts were highly developed in Egypt and 
other nations of antiquity, and that in Egypt in particular the 
professional knowledge of metallurgy and similar processes was 
practically the monopoly of the priesthood and the Crown. On 
the other side of the Mediterranean, the Greeks had burst into 
an efflorescence of intellectual effort and had produced two 
theories, viz. those of Aristotle on the constitution of the world, 
and of the Atomists on the minute structure of matter, which 
will emerge again later in our story. Plato also had evolved a 
philosophical system which continued to develop after his 
death, and reached its culminating point in the Neo-Platonism 
of Alexandria in the early centuries of the Christian era. 

At Alexandria, Egyptian practice and late Greek speculation 
fused, the occultism of the Gnostics and the transcendentalism 
of the Neo-Platonists leading to highly imaginative theoretical 
explanations of metallurgical processes and mineralogical 

4O A Retrospect 

observations. The transmutation of metals a superficial inter- 
pretation of Egyptian metallurgical facts gained universal 
credence, and the philosopher's stone was a means whereby this 


transmutation could be effected. The new science or art was 
called Chemeia, whence in Muslim days the name al-chemy and 
later still our chemistry. With the degeneration of Hellenic 
culture, chemistry itself became more and more divorced from 

The Rise of Islam 41 

fact, until in the seventh century A.D. it was almost completely 
an occult art. Yet among the Alexandrian chemists there must 
have been many capable men, who undoubtedly advanced the 
practical side of the subject. 

1 6. The Rise of Islam 

ON 8 June, A.D. 632, the Prophet Muhammad died, having 
accomplished the marvellous task of uniting the tribes of Arabia 
into a homogeneous and powerful nation. Exactly a century 
later, in A.D. 732, the victorious march of the Muslim armies was 
stemmed at Poitiers (France) by Charles the Hammer. In the 
interval, Persia, Asia Minor, Syria, Palestine, Egypt, the whole 
North African littoral, Gibraltar and Spain had been conquered 
by the forces of Islam, and a new civilization had been estab- 
lished. 'The stupendous conquests which laid the foundations 
of the Arab Empire/ says Sir Thomas Arnold, 

were certainly not the outcome of a holy war, waged for the 
propagation of Islam, but they were followed by such a vast 
defection from the Christian faith that this result has often been 
supposed to have been their aim. Thus the sword came to be 
looked upon by Christian historians as the instrument of Muslim 
propaganda, and in the light of the success attributed to it the 
evidences of the genuine missionary activity of Islam were obscured. 
But the spirit which animated the invading hosts of Arabs who 
poured over the confines of the Byzantine and Persian empires, was 
no proselytizing zeal for the conversion of souls. On the contrary, 
religious interests appear to have entered hut little into the con- 
sciousness of the protagonists of the Arab armies. This expansion 
of the Arab race is more rightly envisaged as the migration of 
a vigorous and energetic people driven by hunger and want, to 
leave their inhospitable deserts and overrun the richer lands of 
their more fortunate neighbours. 

The Arabs quickly assimilated the culture and knowledge of 
the peoples they conquered, while the latter in turn Persians, 
Syrians, Copts, Berbers, and others adopted the Arabic 
language. The nationality of the Muslim thus became sub- 
merged, and the term Arab acquired a linguistic sense rather 

42 The Rise of Islam 

than a strictly ethnological one. By an 'Arab', indeed in this 
book we shall understand an Arabic-writing Muslim of whatever 
race, unless definite indication is given that the word is used in 
its narrow sense. 

As soon as the disturbance of military operations had sub- 
sided, the Arabs began to encourage learning of all kinds. 
Schools, colleges, libraries, observatories and hospitals were 
built throughout the empire, and were adequately staffed and 
endowed. Scholars were invited to Damascus and Baghdad 
without distinction of nationality or creed. Greek manuscripts 
were acquired in large numbers and were studied, translated 
and provided with scholarly and illuminating commentaries. 
The old learning was thus infused with a new vigour, and the 
intellectual freedom of the men of the desert stimulated the 
search for knowledge. 

The oft-repeated story that the Arabs burnt the library at Alex- 
andria is a fable that appears for the first time in the thirteenth 
century, some six hundred years after the supposed event. It 
carries its own refutation in the circumstantial detail provided to 
give 'verisimilitude to an otherwise bald and unconvincing 
narrative ' ; we are told that the books were used as fuel in the baths 
at Alexandria and that the supply was sufficient for six months. 
Now we happen to know that there were 4,000 baths in the town, 
and, on a very moderate estimate, to heat them for six months 
would have required a library of no fewer than 72,000,000 volumes! 
The truth is that the library had been destroyed long before the 
Muslim conquest. 

In early days jit least, the Muslims were eager seekers after 
knowledge, and Baghdad was the intellectual centre of the world. 
A celebrated historian has justly remarked that what charac- 
terized the school of Baghdad from its inception was its 
scientific spirit. Proceeding from the known to the unknown; 
taking precise account of phenomena ; accepting nothing as true 
which was not confirmed by experience, or established by 
experiment such were the fundamental principles taught and 
acclaimed by the then masters of the sciences. 


1 7. The Origins of Alchemy in Islam 

TRADING operations between Arabia and the countries on its 
boundaries, particularly Syria, must have resulted in the in- 
filtration of the main doctrines and practices of alchemy even in 
thejahiliyya, or 'Time of ignorance', as Muslim writers describe 
pre-Islamic days. Yet the knowledge thus gained roused little 
general attention and no records of it remain ; the Arabs them- 
selves assert that alchemy was first studied in Islam by Khalid 
ibn Yazid, though deferential tradition ascribes a knowledge of 
the Art to Muhammad and to his cousin and son-in-law the 
Caliph Ali. 

The Jews came to the Prophet, says the story, and asked him con- 
cerning alchemy. He said, 'If I will that the camels from Tihama 
come to me laden with gold and silver, it is so : lift ye up the reed 
mat. ' They lifted it and saw a large quantity of gold. Then said 
the Jews, 'That and the like thereof can the magicians also do/ 
The Prophet replied, 'If I reveal the Art to you, will ye then accept 
Islam?' They answered him, 'Yea'. Thereupon the Prophet said, 
'It consists in common gold, lead, bitter salt and ordinary quick- 
silver; yet will ye not believe!' We can, perhaps, hardly blame them. 

It is evident from stories such as this that the Muslims very 
quickly became acquainted with alchemy, and no doubt their 
information reached them from very many different sources. It 
was, however, through the city of Alexandria that the first real 
introduction of the art to Islam took place, if the unanimous 
tradition of the Arabs themselves is to be believed. The main 
thesis is probable enough Alexandria, as we have already seen, 
was a centre of alchemy and other occult arts and sciences but 
the details given by native writers are open to doubt. Yet the 
story is worth repeating, for it tells us what Muslim chemists 
believed about the origin of alchemy in Islam and may well be 
based upon some foundation of truth : 

There lived in Alexandria a Christian monk named Marianus, 
an ascetic and an adept in alchemy. The young Arab prince, 
Khalid ibn Yazid (died 704 A.D.), heard of the fame of Marianus 
and summoned him to Damascus to expound the science of the 

44 The Origins of Alchemy in Islam 

transmutation of the metals. After much persuasion, Marianus 
came and instructed Khalid in the art of preparing the Elixir ; 
whereupon Khalid became so enamoured of alchemy that he 
caused numbers of Greek alchemical works to be translated into 
Arabic, and seems to have devoted a great deal of time to the 
investigation of the subject. There is no statement of the actual 
works translated, but we may suspect them to have been books 
of Zosimos, 'Democritus', 'Ostanes', and similar writers, their 
general characteristics being a love of mystification and a re- 
markable reluctance to state any definite facts. None of 
Khalid's own writings on alchemy appears to be extant, if we 
except certain poetical fragments of doubtful authenticity; 
these lead one to the conclusion that the loss is not a serious one, 
as they show only too clearly that their author was quite un- 
critical and credulous. Khalid's services to chemistry, indeed, if 
he ever performed any, lie in the fact that by his enthusiasm and 
example he led better men to its study, rather than in any 
advance of either a theoretical or a practical nature. This is the 
picture given of him in a tenth-century Muslim encyclopaedia : 
The first to investigate the books of the ancients upon alchemy was 
Khalid ibn Yazid ibn Mu'awiyya. He was an orator, a poet, 
eloquent, and full of enthusiasm and judgement. He was the first 
to have translated the [ancient] books of medicine, astrology and 
alchemy. Of a generous nature, it is said that he replied thus to one 
who had reproached him with devoting most of his life to the pur- 
suit of alchemy: 'All my researches have for their sole aim the 
enrichment of my brethren and companions. I had hoped for the 
Caliphate, but it has been taken from me, and I have found no 
compensation except in attempting to reach the utmost limits of 
the Art. I wish to render every one whom I know, or who has 
known me though it were for but a single day independent of 
the necessity of soliciting favours from a prince/ It is said (Allah 
knows best whether it is true!) that Khalid was successful in his 
alchemical undertakings. He wrote on the subject a number of 
treatises and tracts and composed much verse on the matter. 

From the same encyclopaedia we can also gather some of the 
names venerated by alchemists in the early days of Islam. Many 




46 The Origins of Alchemy in Islam 

are those of historical personages, others are mythical and others 
cannot be identified. First comes Hermes (Thoth), followed by 
Agathodemon; then come Plato, Zosimos, Democritus, Herac- 
lius, Ostanes, Alexander, Mary the Jewess and many more, the 
main interest in the list being the indication it affords that 
alchemy was widely studied, even if not very intelligently, and 
that the habit of falsely attributing works on the Art to any 
great man whose authority was considered desirable had already 
'become established. 

We may be quite certain that, in the main, Muslim alchemy 
was derived from the Greek. The frequency with which Greek 
authors are quoted, the numerous theories that are common 
to both Greek and Arabic alchemy, and the large number 
of Arab technical terms clearly taken over from Hellenic 
treatises (e.g. hayuli* atisyus, 2 athalia? iksir^ qambarf] prove 
beyond doubt the affiliation of Muslim and Greek alchemy. 
The transmission was made partly through direct contact in 
Egypt, partly through the medium of Syrian Christian trans- 
lators, and partly by way of Persia. There are unmistakable 
traces of Persian influence, manifested distinctly by linguistic 
affinities in technical names and usages and in names of minerals. 
These traces are sufficiently well marked to render it probable 
that Persia was, indeed, one of the main channels through which 
alchemy came to Islam; and it is not without interest to note 
that many of the principal Muslim alchemists were Persians. 

It has already been observed that Chinese alchemy has so 
much in common with Greek and Arabic alchemy as to afford 
support to the hypothesis that all three had a common origin ; 
and there is some reason to believe that the Chinese practised 
a kind of alchemy long before the days of Islam (see p. 25). The 
remote origins of Arabic alchemy are therefore still to some 
extent uncertain, but there is very little to recommend the 
suggestion that the Arabs received any direct introduction to 
alchemy from the Chinese. Whatever may be the cause of the 
similarity between Chinese, Greek and Muslim alchemical ideas, 

4 fijpiov. 5 Ktvvdf}api. 

The Origins of Alchemy in Islam 47 

Arabic alchemy is for the most part a direct legacy from the 
Greek, and to a less extent from Persian, Chaldean and other 
sources. A further factor to be considered in this connexion is 
the practical knowledge possessed by the craftsmen of the 
nations with which the Arabs had at one time or another come 


V^v; - ; 


into contact. The skill attained by the technical workers of 
ancient Egypt and Assyria has already been described, and it is 
noteworthy that many Assyrian mineral and other names are to 
be found in Arabic treatises on alchemy. Not the least in- 
teresting is the word abaru, meaning the metal extracted from 
collyrium, that is, lead or antimony, which occurs very fre- 
quently in Arabic alchemy and even passed over into medieval 
Latin treatises. 

Briefly, it is reasonable to suppose that, although the main 
source of alchemy in Islam is certainly Greek, the Greek know- 
ledge and theories found awaiting them a fairly extensive 
acquaintance with certain practical arts ; and that they were also 
admixed sooner or later with fresh material from surrounding 
countries and even perhaps from India and China. 

48 The Origins ot Alchemy in Islam 

In the actual process of transmission of Greek alchemy to 
Islam, there is much evidence to show that a good deal of the 
work of translation was carried out by Syrian Christians. 
Berthelot, indeed, goes so far as to maintain that Syrian scholars 
played the chief part in handing on Greek learning to the Arabs. 
'They already played an important part', he says, 'as inter- 
mediaries between the Persian sovereigns und the Emperors of 
Constantinople, but their authority became even greater when 
the Arabs had conquered Persia and Syria. The caliphs sought 
them particularly on account of their medical skill, but they 
played many parts, for we find them as physicians, civil and 
military engineers, astrologers, treasury officials, town governors, 
etc. The importance they acquired was very favourable to the 
development of scientific culture; now all their science came 
from the Greeks, and it was through them that Greek doctrine 
passed on to the Arabs/ 

This estimate is probably exaggerated. It seems possible that 
even in the eighth century many Muslim scholars could read 
Greek, and were thus in a position to study Greek authors in the 
original. Moreover, as was stated above, the transmission of 
Greek knowledge to Islam by way of Persia was by no means 
negligible, and was of special importance in medicine, alchemy 
and astrology. The great Academy at Jundi-Shapur in Khuzis- 
tan (S.W. Persia) was still flourishing in the days of the 'Abbasid 
caliphs, and the Persianized form of Greek philosophy and 
medicine taught there had great influence upon the progress of 
Muslim learning. Still another channel through which Hellenic 
wisdom passed to Islam was the town of Harran in Mesopotamia. 
Harran had been a home of Greek culture ever since the days of 
Alexander the Great. It was inhabited by Syrian pagans who 
later became known to the Arabs as Sabians; they were star- 
worshippers and enthusiastic astrologers. As linguists they 
possessed unusual skill, and the ease with which they learnt to 
speak Arabic put them into an exceptionally favourable position 
for teaching their eager neighbours. In spite of their paganism 
they found favour at the Court of Baghdad, no doubt on account 

Jabir ibn Hayyan 49 

of their scholarship, but to ensure their personal safety they dis- 
covered it necessary to pay a considerable sum in the way of 
bribes to the conscientious Muslim officials. It is probable that 
Harran also transmitted much of the old Babylonian lore in 
addition to the Hellenic culture. 

1 8. Jabir ibn Hayyan 

THE greatest chemist of Islam has long been familiar to Western 
readers under the name of Geber, which is the medieval render- 
ing of the Arabic Jabir. For our knowledge of Jabir 's life, we 
now have a not insignificant collection of data, and can recon- 
struct his figure with reasonable accuracy. Although much is 
conjectural, the following may be taken to represent, in brief, 
what we know of him. 

In A.D. 638 the Caliph Omar was visited at Medina by a 
deputation of Arabs from Al-Meda'in, a town on the Tigris 
that they had recently conquered. The Caliph was startled by 
their sallow and unwholesome look, and asked the cause. They 
replied that the air of the town did not suit the Arab tempera- 
ment, and the Caliph therefore ordered inquiry for some more 
healthy and congenial spot. A plain on the banks of the 
western branch of the Euphrates was finally chosen, and there 
the city of Kufa was founded. The new town suited the 
Arabs well, and to it they accordingly migrated in great 
numbers. But the dwellings were at first made of reeds, and 
fires were frequent, so after a particularly disastrous conflagra- 
tion the city was rebuilt with less inflammable material, and the 
streets were laid out in regular lines. In orderly fashion, be- 
fitting a military station, the various Arab tribes were settled in 
particular quarters of the town no doubt with a view to the 
prevention of civil commotion. 

One of the tribes whose members were present at Kufa in 
sufficient numbers to be assigned a definite quarter was that 
known as Al-Azd, a celebrated tribe of South Arabia. From this 
tribe there sprang, towards the end of the seventh century A.D., 
a man named Hayyan, who carried on the business of a druggist 

2613-4 E 

50 Jabir ibn Hayyan 

at Kufa. His life would appear to have been uneventful until 
the early years of the eighth century, when we find that he 
espoused the cause of the powerful 'Abbasid family, who were 
trying to overthrow the reigning Caliph of the house of Umayya 
in order to usurp his place. To further their plans, the 'Abbasids 
engaged in extensive political propaganda, and Hayyan was sent 
as an emissary to Persia on this business. It was while he and his 
wife were at the town of Tus, in Khorasan, near the modern 
Meshed, that his son Jabir was born, probably in the year 
A.D. 721 or 722. Shortly afterwards, Hayyan was arrested by 
agents of the Caliph and was subsequently executed. 

The now fatherless Jabir ibn [son of] Hayyan was sent to 
Arabia, perhaps to his kinsmen of the Azd tribe, to be cared for 
until he was old enough to fend for himself. Whilst in Arabia, 
he studied the Koran, mathematics and other subjects under 
a scholar named Harbi al-Himyari, of whom unfortunately we 
have no record. Meanwhile the 'Abbasids, in whose service 
Jabir 's father had lost his life, succeeded in achieving their 
object. In A.D. 748 they overthrew theUmayyads and themselves 
assumed the Caliphate, so that Hayyan had not died in vain. It 
was under the 'Abbasid caliphs, the most famous of whom was 
Harun al-Rashid, that Islamic civilization reached its zenith. 

During the period in which these political changes were 
taking place, Jabir appears to have won the friendship of the 
Imam Ja'far al-Sadiq, one of whose disciples he became. Ja'far 
was a man held in very high esteem by a section of Muslims 
known as the Shi'ites, and the Shi'ites themselves had been 
active in support of the 'Abbasid cause. These facts, coupled 
with the recollection of Hayyan *s activity in the same direction, 
enable us to understand how Jabir in middle life came to be 
welcomed at the Court of Harun al-Rashid at Baghdad. He does 
not seem to have had much personal contact with the sovereign 
himself, but he was on intimate terms with the Caliph's all- 
powerful ministers the Barmecides, some of whom figure in The 
Thousand and One Nights. 

On one occasion we find him accompanying his patrons to the 

Jabir ibn Hayyan 51 

slave-market, to buy handmaids, while on another he describes 
a cure he effected in Yahya the Barmecide's household. 

Yahya ibn. Khalid [says Jabir] possessed a very valuable hand- 
maiden, unequalled in beauty and perfection and deportment and 



intelligence and accomplishments. One day she fell ill and though 
she drank medicine it failed to cure her, and she rapidly grew 
worse and finally became delirious. A messenger came to Yahya 
with the news and he asked me what I advised. I had not seen her 
and thought she might be poisoned, so I recommended the applica- 
tion of cold water. This treatment was of no avail, so I ordered 
them to poultice her abdomen with heated salt and to chafe her 
feet. As she still grew worse, Yahya at last asked me to go and see 
her, and I found her at the point of death from some obscure 


52 Jabir ibn Hayyan 

disease. Now I had a certain elixir with me, so I gave her a draught 
of two grains of it in three ounces of oxymel, and, by Allah ! the 
sickness departed from the damsel, and in less than half an hour 
she was as well as ever. And Yahya fell at my feet and kissed them, 
hut I said, 'Do not so, O my brother.' And he asked me about the 
uses of the elixir, and I gave him the remainder of it and explained 
how it was employed, whereupon he applied himself to the study 
of science and persevered until he knew many things; but he was 
not so clever as his son Ja'far. 

Al-Jildaki, a Muslim chemist who lived in the fourteenth 
century (see p. 81), tells us that, through the medium of the 
vizier Ja'far the Barmecide, Jabir was brought into relation with 
the Caliph Harun al-Rashid, 'for whom he wrote a book on the 
noble art of alchemy entitled The Book of the Blossom. In it he 
described wonderful experiments of a very elegant technique'. 
We learn also that it was through the efforts of Jabir that the 
second importation of Greek scientific books from Constanti- 
nople was made, the first being that which was made under the 
auspices of Khalid ibn Yazid some three-quarters of a century 
earlier. It was not until the reign of Al-Ma'rnun (A.D. 813- 33) 
that the process reached its maximum development ; this Caliph 
sent a deputation to the Roman Emperor Leo the Armenian 
with a request for Greek books for translation into Arabic, and 
built the celebrated 'House of Wisdom' or Baitifl-Hikma at 
Baghdad, in which the translators, together with astronomers 
and other scientists, were installed. 

It seems therefore, that while Jabir's main interests lay in 
chemistry, he was a widely-read scholar, and probably had some 
knowledge of Greek. His own list of his writings, which has 
come down to us at second hand in the Kitab al-Fihrist of Ibn 
al-Nadim (about A.D. 1000), shows that, in addition to books on 
chemistry, he wrote others on a variety of subjects a fact that 
need not surprise us when we remember the vast extent of the 
intellectual treasures now becoming available to the Muslims 
through their introduction to Greek learning by way of Jundi- 
Shapur, Harran, Alexandria and other centres of Hellenic 

54 Jabir ibn Hayyan 

culture. Thus we find that he wrote a commentary on Euclid 
and the Almagest of Ptolemy ; he knew some of the writings or 
views of Plato, Socrates, Aristotle, Hippocrates, Empedocles, 

Pythagoras and Democri- 
tus; he wrote a treatise on 
Mirrors, another on Logic, 
and another on the art of 
Poetry; he interested him- 
self in the newly-developed 
mystical system of Sufi-ism, 
and he studied the ideas of 
Apollonius of Tyana. He 
was thus a man of culture 
and scholarship and not a 
petty mystagogue or char- 
latan; we can indeed be 
certain that the Barme- 
cides a pretty shrewd 
and level-headed family 
would otherwise not long 
have tolerated him. 

When Jabir first went to 
Baghdad to live we do not 
know, but for a part of his 
life he lived at Kufa. Here 
he had a laboratory, which 
was rediscovered, about two 
Fig. 18. PAGE OF ONE OF JABIR'S centuries after his death, 

CHEMICAL WORKS IN ARABIC during ^ demo lition of 

some houses in the quarter of the town known as the Damascus 
Gate. Among other things brought to light were a mortar and 
a large piece of gold, 'of which', says the chronicler slyly, 'the 
King's Chamberlain took possession'. 

In A.D. 803 Harun al-Rashid finally tired of the Barmecides, 
who had .grown so powerful as to be a continual menace to him, 
and executed one of them and banished the rest. Jabir, we are 

if ", 



56 Jabir ibn Hayyan 

told, was involved in the disgrace of his patrons, and fled to Kufa, 
where he spent the remainder of his life in retirement. The date 
of his death is uncertain. According to Al-Jildaki, who was 
usually very well informed about the chemists of Islam, Jabir 
survived until the days of Al-Ma'mun, who succeeded in 
A.D. 813, and the last public act of his life was to help to persuade 
the Caliph to nominate as his successor the young Shi'ite Imam 
Ali al-Rida, in A.D. 817. We hear nothing of him afterwards, so 
we may presume that he died about that time, at the ripe age of 
95. It is, of course, possible that the last tradition is mistaken, 
but the quality and quantity alike of Jabir 's books are such that 
no man who died young would have had time to write them. 

The idea that the transmutation of the metals was possible had 
the excellent merit of provoking incessant experiment, but un- 
fortunately the alchemists were always prone to theorize to an 
inordinate extent. Moreover, at Alexandria, the mystical 
beliefs of the Gnostics and the Neo-Platonists however 
admirable and attractive in themselves had a very detrimental 
effect upon experimental science. Alchemy thus became less 
and less a matter for experimental research and more and more 
the subject of ineffable speculation and superstitious practice, 
not to say fraudulent deception. 

In such an atmosphere Jabir began his study, and it is not 
surprising to find that he never completely shook off the effects. 
About a hundred of his books are extant, and many of them seem 
to us of the twentieth century to be confused jumbles of puerile 
superstition. The peculiar characteristic of Jabir is, however, 
that in spite of his leanings to mysticism and superstition, he 
more clearly recognized and stated the importance of experiment 
than any other early chemist, and made noteworthy advance in 
both the theory and practice of chemistry. 

One of his chief contributions to the theory of chemistry 
lies in his views upon the constitution of the metals. To under- 
stand his conceptions properly, we must hark back to Aristotle, 
whose philosophy of nature was universally accepted in its main 
principles by the scientists of Islam. According to Aristotle, it 

Jabir ibn Hayyan 57 

will be remembered, all substances are composed of the four 
* elements' fire, air, water, and earth, which are themselves inter- 
convertible. The immediate constituents of minerals and metals 
are two exhalations, one an 'earthy smoke' and the other a 
'watery vapour' ; the former consists of small particles of earth 
on the way to becoming fire, while the latter consists of small 
particles of water on the way to becoming air. Neither exhala- 
tion is ever entirely free from some admixture of the other. 
Stones and other minerals are formed when the two exhalations 
become imprisoned in the earth, the dry or smoky exhalation 
predominating ; metals are formed under similar circumstances 
if the watery exhalation predominates. 

Jabir accepted this theory of the constitution of metals, but 
appears to have regarded it as too indefinite to explain observed 
facts or to afford a guide to practical methods of transmutation. 
He therefore modified it in such a fashion as to make it less 
vague, and the theory he suggested survived, with some altera- 
tions and additions, until the beginning of modern chemistry in 
the eighteenth century. The two exhalations, he believed, when 
imprisoned in the bowels of the earth, are not immediately 
changed into minerals or metals, but undergo an intermediate 
conversion. The dry or smoky exhalation is converted into 
sulphur and the watery one into mercury, and it is only by the 
subsequent combination of sulphur and mercury that metals 
are formed. The reason of the existence of different varieties 
of metals is that the sulphur and mercury are not always pure, 
and that they do not always combine in the same proportion. 
If they are perfectly pure and if, also, they combine in the most 
complete natural equilibrium, then the product is the most 
perfect of metals, namely gold. Defects in purity or proportion, 
or both, result in the formation of silver, lead, tin, iron, or copper, 
but since these metals are essentially composed of the same 
constituents as gold, the accidents of combination may be 
removed by suitable treatment. Such treatment is the object of 

To the modern mind it will at once occur that the above 

58 Jabir ibn Hayyan 

theory might easily have been tested by experimental attempts 
to obtain metals by the combination of sulphur and mercury. 
We may be quite sure that so obvious a deduction was not 
overlooked by Jabir, for in one of his books he describes such an 
experiment and states that the product was 'the red stone known 
to men of science as cinnabar' the mercuric sulphide of our 
text-books of chemistry ^ From observations such as this, Jabir 
was forced to the conclusion that the sulphur and mercury of 
which metals are composed are not the well-known substances 
that go by these names, but hypothetical substances to which 
ordinary sulphur and mercury form the closest available 
approximations. That this theory has all the bad qualities 
which Lavoisier found in the theory of phlogiston several 
hundred years later cannot be denied, but it represented a dis- 
tinct advance upon any previous theory, and satisfied the 
intellectual curiosity of many brilliant scientists for a very 
lengthy period. The phlogiston theory itself, which, in spite 
of its shortcomings, has been described as 'the lamp and 
guide of chemists' during the eighteenth century and 'the time- 
honoured and highest generalization of physical chemistry for 
over half a century/ was a direct descendant of Jabir's theory of 
the constitution of metals, and thus ultimately of Aristotle's 
theory of the two exhalations. 

On the practical side, Jabir was acquainted with the usual 
chemical operations such as crystallization, calcination, solution, 
sublimation, reduction, &c., and often describes them. Of more 
interest, however, is the fact that he attempts to understand the 
changes that go on in these processes, and frequently gives his 
opinions as to their aims. His method of reducing calces 
[metallic oxides] is illustrated by the following quotation : 

Take a pound of litharge and a quarter of a pound of soda and 
powder each well. Then mix them together and make them up 
into a paste with oil and heat in a descensory. The metal will 
descend pure and white. 

To calcination, i.e. the conversion of a metal into a powder by 

Jabir ibn Hayyan 59 

oxidation or otherwise, he devoted a complete book, from which 
the passage below is quoted : 

Souls and spirits [i.e., volatile substances like sulphur and sal- 
ammoniac] will not sustain calcination, since the latter can be 
effected only with a very hot fire; now spirits will not sustain 
a very hot fire as they are volatile and fly away from it. Moreover, 
the aim of calcination is nothing more than the removal of im- 
purities from metals and their complete combustion, so that the 
metals may be purified and remain unadulterated and unsullied; 
in a spirit, however, there is no necessity for the same treatment as 
in a metal, and all that is needed is the first process in calcination 
[i. e., gentle heating] , when the same effect is produced on the spirit 
as [complete] calcination effects on the metals, namely, full 
purification. As for the process which is to spirits what calcination 
is to metals . . . thou wilt find it to be sublimation. 

As I have now made clear the aim of calcination I will next 
speak of its various forms, for each metal is calcined in a different 
way from the others. This is because among the metals are found 
some which are already pure, such as gold ; in this case the object 
of calcination is to convert the metal into a fine powder so that it 
may be enabled to combine and enter into union with the sublimed 
spirits, and also to dissolve. The same applies to silver, but silver 
is slightly impure, so that it needs purification as well as conversion 
into a fine powder. 

As for the rest of the metals, that is excluding the two above- 
mentioned, they indeed all require calcination both for purification 
and also for converting them into powder ; and the same is true for 
those minerals which are infusible, according to their degree of 

The practical applications of chemistry were not neglected. 
Jabir describes processes for the preparation of steel and the 
refinement of other metals, for dyeing cloth and leather, for 
making varnishes to waterproof cloth and to protect iron, for the 
preparation of hair-dyes and so on. He gives a recipe for making 
an illuminating ink for manuscripts from * golden' marcasite, to 
replace the much more expensive one made from gold itself, and 
he mentions the use of manganese dioxide in glass-making. He 
knew how to concentrate acetic acid by the distillation of 

60 Jabir ibn Hayyan 

vinegar, and was also acquainted with citric acid and other 
organic substances. It is, indeed, abundantly evident that his 
experimental work was skilful and extensive; and that he 
realized the importance of experiment in chemistry may be 
witnessed by the following characteristic remarks : 

The first essential in chemistry is that thou shouldest perform 
practical work and conduct experiments, for he who performs not 
practical work nor makes experiments will never attain to the least 
degree of mastery. But thou, O my son, do thou experiment so 
that thou mayest acquire knowledge. 

Scientists delight not in abundance of material ; they rejoice only 
in the excellence of their experimental methods. 

Perhaps his most useful discovery was that of nitric acid, the 
preparation of which is described for the first time in one of his 
books entitled The Chest of Wisdom. 

19. The Latin Works of Jabir or Geber 

SOME of Jabir 's books, for example, The Book of Seventy and 
The Book of Mercy, were translated into Latin in the Middle 
Ages, and in the two cases mentioned both the Arabic and Latin 
versions are extant. There are, however, certain other Latin 
works, entitled The Sum of Perfection, The Investigation of 
Perfection, The Invention of Verity, The Book of Furnaces, and 
The Testament, which pass under his name but of which no 
Arabic original is known. A problem which historians of 
chemistry have not yet succeeded in solving is whether these 
works are genuine or not. Many scholars have regarded them 
as European forgeries of the twelfth or thirteenth centuries, 
basing their conclusion upon the following arguments : 

1. No Arabic originals have been found. 

2. The contents of the books differ from the contents of 
Arabic books undoubtedly written by Jabir. 

3 . The style of the books is (a) different from that of Jabir 
and (b) characteristic of the Schoolmen. 

4. The Latin author devotes much space to the refutation of 
those who disbelieve in the possibility of transmutation ; now 

Jabir ibn Hayyan 61 

this disbelief, says one authority, 'appeared only in the twelfth 

We may consider these arguments in order. As to the first, 
the fact is undoubted, but the recent discovery of the Arabic text 
of The Book of Seventy does much to diminish its weight. As 
to the second, it is true that the contents of The Sum of Per- 
fection and the books which usually accompany it cannot be 
paralleled in any single known Arabic book of Jabir's. But this 
fact takes on a different aspect when we read the opening words 
of The Sum of Perfection, viz., 'Our whole Science of Chymistry, 
which, with a diverse Compilation, out of the Books of the 
Ancients, We have abbreviated in our Volumes, We here reduce 
into one Sum/ If this passage truly represents the author's 
procedure, what we should look for among the extant Arabic 
works is not necessarily one which in itself contains all the facts 
described in The Sum of Perfection', we should rather examine 
the contents of all of them and consider whether The Sum of 
Perfection might veritably have been composed of facts scattered 
throughout them. Many of Jabir's books still existing have 
not yet been studied, but, with a few notable exceptions, no 
information is given in The Sum of Perfection^ &c., which is not 
to be found in one or other of the Arabic works. It follows 
that the second argument is no more conclusive than the first. 

The third argument is based upon the contrast in style 
between The Sum of Perfection, &c., and genuine Arabic works 
of Jabir. That a contrast does exist it would be idle to deny, but 
the genius of the Latin language is so different from that of 
Arabic that style is inevitably more or less obscured in the process 
of translation. Nevertheless, the objection is a weighty one, for 
the present writer knows no Arabic book of Jabir's so systematic- 
ally arranged as The Sum of Perfection. On the other hand, to 
those versed in the writings of the Muslim alchemists, there are 
clear traces of an ultimate Arabic origin in The Sum of Perfection 
as well as in the other books usually found with it. That the style 
of these books is characteristic of the Schoolmen is a statement 
that need not be taken too literally ; it is based upon the elaborate 

62 Jabir ibn Hayyan 

refutation which Geber makes of his opponents, and can be most 
conveniently considered in that connexion. 

The fourth argument against the authenticity of the Latin 

n Wvt- 

' " 

r<3U> f^ 

Fig. 20. EARLY MS. OF GEBER'S Investigation of Perfection 

books is that Geber formally argues at great length against 
those who disbelieve in the possibility of transmutation, first 
describing the reasons they advance and then proceeding to 
refute them seriatim. This manner is, of course, typical of the 

Jabir ibn Hayyan 63 

Schoolmen, but it is by no means confined to them and cannot 
be regarded as a reliable criterion. In the next place, the state- 
ment that disbelief in the possibility of transmutation arose only 
in the twelfth century is entirely incorrect, as we shall see later. 
In his Arabic works Jabir definitely refers to those who are in- 
credulous, and his successor Razi went so far as to write a 
book to confound them. 

The authenticity of the books under consideration is therefore 
still uncertain. It is possible that they are genuine translations 
from Arabic books of Jabir ; or that they are genuine translations 
from Arabic books of other chemists ; or that they are summaries, 
made in medieval Europe, of Jabir's Arabic books; or that they 
are medieval European forgeries made by an unknown author 
and merely fathered upon Jabir in order to ensure a favourable 
reception. Whatever the future may disclose concerning them, 
we may safely say that they are not unworthy of Jabir and that 
he is worthy of them ; and that we know of no other chemist, 
Muslim or Christian, who could for one moment be imagined 
to have written them. 1 

20. Razi 

AFTER the death of Jabir, nearly a century elapsed before Islam 
produced a worthy successor. History records a few alchemists 
in the interval, but it is only with the Persian chemist and 
physician Abu Bakr Muhammad ibn Zakariyya al-Razi (known 
to the West as Rhazes) that Jabir's great example is successfully 
followed. 2 

According to one of his biographers, Razi was born in A.D. 866 
at Ray, an ancient town on the southern slopes of the Elburz 
Range that skirts the south of the Caspian Sea. In his early 
youth he devoted himself to the study of music, literature, 
philosophy, manichaeism, magic and alchemy, and it was only 

1 It should, however, be stated that the general opinion of those best 
qualified to judge is that the Latin works are not authentic. The present 
writer is practically alone in believing that they may be. 

2 For much in this section, the writer is indebted to the researches of 
Principal H. E. Stapleton, of Calcutta. 

64 Razi 

after his first visit to Baghdad, when he was at least 30 years of 
age, that he seriously took up the study of medicine under the 
well-known doctor AH ibn Sahl (a Jewish convert to Islam, 
belonging to the famous medical school of Tabaristan or 
Hyrcania). Razi showed such skill in the subject that he quickly 
surpassed his master, and wrote no fewer than a hundred 
medical books. He also composed 33 treatises on natural science 
(exclusive of alchemy), 1 1 on mathematics and astronomy, and 
more than 45 on philosophy, logic and theology. On alchemy, 
in addition to his Compendium of Twelve Treatises and Rook of 
Secrets, he wrote about a dozen other books, two of which were 
refutations of works by other authors in which the possibility of 
alchemy had been attacked. 

As to the man himself, one of the inhabitants of Ray who 
recollected Razi described him as a man with a large square head. 
He used to take his seat in the lecture room, with his own pupils 
next him, and the pupils of these men behind them, and, behind 
these again, other pupils. Whenever any one came with a 
question, he used first to ask the back row. If they could answer, 
he went away; but, if not, he used to pass on to the others, and 
they, in their turn, if they could give a correct answer, tried to 
satisfy him ; otherwise Razi would speak on the subject himself. 
He was a liberal and generous man, and so compassionate to the 
poor and sick that he used to distribute alms to them freely and 
even nurse them himself. He was always reading or copying, 
and I never visited him (said the narrator) without finding him 
at work on either a rough or a fair copy. His eyes were always 
watering 'on account of his excessive consumption of beans', and 
he became blind towards the end of his life. He died in his 
native town on 26 October, A.D. 925, at the age of 60 years and 
2 months. 

Razi is of exceptional importance in the history of chemistry, 
since in his books we find for the first time a systematic classifica- 
tion of carefully observed and verified facts regarding chemical 
substances, reactions and apparatus, described in language 
almost entirely free from mysticism and ambiguity. While he 


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G C ca^ 

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66 Razi 

perhaps never attained to the genius of Jabir of whom he 
speaks with admiration and reverence his clear and orderly 
habit of thought and expression made his work easily intel- 
ligible and of permanent value. Razi's scheme of classifica- 
tion of the substances used in chemistry shows such a sound 
chemical insight that it may be reproduced here (page 65). 

Razi gives also a list of the apparatus used in chemistry. This 
consists of two classes: (i) instruments used for melting metals, 
and (ii) those used for the manipulation of substances generally. 
In the first class were included the following: 

Blacksmith's hearth Tongs 

Bellows Shears 

Crucible Hammer or Pestle 

Descensory File 

Ladle Semi-cylindrical iron mould 

The second class included : 

Cucurbite Flasks Cylindrical stove 

Alembic Phials Potter's Kiln 

Receiving flask Jars Chafing-dish 

Aludel Cauldron Mortar 

Beakers Sand-bath Flat stone mortar 

Glass cups Water-bath Stone roller 

Shallow iron pan Large oven Round mould 

Sieve Hair-cloth Glass funnel 

Heating-lamps Filter of linen Dish 

It will be observed that the list was comprehensive, but Razi 
completes the subject by giving details of making composite 
pieces of apparatus, and in general provides the same kind of 
information as is to be found nowadays in manuals of laboratory 

Like Jabir, Razi was a firm believer in the possibility of 
transmutation, and Stapleton describes his scheme of procedure 
approximately as follows. The first stage consisted in the 
cleansing and purification of the substances employed, by means 
of distillation, calcination, amalgamation, sublimation and other 

Abu Mansur Muwaffak 67 

processes. Having freed the crude materials from their im- 
purities, the next step was to reduce them to an easily fusible 
condition. This was done by an operation known as ceration, 
that resulted in a product which readily melted, without any 
evolution of fumes, when dropped upon a heated metal plate. 
The next step was to bring the derated ' products to a further 
state of disintegration by the process of solution. The solutions 
of different substances, suitably chosen in proportion to the 
amount of 'bodies', * spirits', &c., they were supposed to possess, 
were brought together by the process of combination. Finally, 
the combined solutions underwent the process of coagulation or 
solidification, the product which it was hoped would result being 
the Elixir. This, as previously explained, was a substance of 
which a small quantity, when projected upon a larger quantity 
of baser metal, would convert the latter into silver or gold. 

From a general study of his chemical works, Stapleton says 
that henceforward Razi must be accepted as one of the most 
remarkable seekers after knowledge that the world has ever 
seen not only 'unique in his age and unequalled in his time', 
but without a peer until modern science began to dawn in 
Europe with Galileo and Robert Boyle. The evidence of his 
passion for objective truth that is furnished by his chemical 
writings, as well as the genius shown by the wide range of books 
he wrote on other subjects, force us to the conclusion that 
with the possible exception of his acknowledged master, Jabir 
Razi was the most noteworthy intellectual follower of the Greek 
philosophers of the seventh to fourth centuries B.C. that mankind 
produced for 1900 years after the death of Aristotle. His supreme 
merit lay in his rejection of magical and astrological practices, 
and adherence to nothing that could not be proved, by experi- 
ment and test, to be actual fact. 

21. Abu Mansur Muwaffak 

THE closing years of the tenth century witnessed the appearance 
3f a remarkable book on pharmacology, written by the Persian, 
Abu Mansur Muwaffak. It is based upon a comprehensive study 

F 2 

68 Avicenna 

of Greek, Indian, Arabian and Persian medicine, and although 
its outlook is primarily that of a physician, it contains much of 
interest to the chemist. Thus Abu Mansur is probably the first 
to make a clear distinction between sodium carbonate (natruri) 
and potassium carbonate, to which he confines the name qali ; 
he mentions that the latter is obtained from the ashes of certain 
plants, and is a white deliquescent salt of a caustic taste. Quick- 
lime he recommends as a depilatory ; for a less vigorous action 
milk of lime may be used. He describes arsenious oxide as a 
pure white powder, and was acquainted with the silicic acid 
(tabashir) obtained from the bamboo. Antimony, he says, is 
a substance of dark colour, but a freshly cut surface of it has 
a fine metallic lustre. Copper, if left exposed to the air, is often 
converted into a green mass similar to malachite; if strongly 
heated in air it yields a black substance [CuO] , which may be 
used to darken the hair. If taken internally, copper compounds 
are poisonous, especially copper vitriol ; so are the compounds of 
lead, particularly white lead, the best sort of which comes from 
Ispahan. Gypsum when heated yields a sort of Mime' which, 
mixed with white of egg, forms a plaster of great service in the 
treatment of fractures of bones. 

Abu Mansur also mentions the distillation of sea-water (an 
operation known to Aristotle or at least to his commentator, 
Alexander of Aphrodisias) : 'I have heard that the crew of a ship, 
when they have no drinking water, obtain a very serviceable 
water, free from saltiness, by the distillation of sea- water/ 

22. Avicenna 

'THE state of the Muslim empire at the end of the tenth century', 
says Carra de Vaux, 'may be represented by that of an un- 
disciplined and stormy feudality, where, under an enervated and 
disorganized central authority, a crowd of vassal powers spring 
up one after another, dominate a part of the empire and are then 
eclipsed. Races and creeds come into conflict, advancing or 
retreating according to the fortunes of the political adventurers 
who represent them. In general, the Arab spirit is in decline; 

Avicenna 69 

the old Persian spirit awakes from time to time, but never quite 
succeeds in freeing itself completely from the chaos, hindered 
as it is by outbursts of barbarism due chiefly to the Turkish 
element. Nevertheless, science pursues its destinies, in the shelter 
of the ephemeral protection afforded it here and there by a few 
princely personages. It is in such circumstances, whose troubled 
and tempestuous character is reflected in his life, that Avicenna 
for the first time gave a clear, ordered and complete expression 
to that calm and grandiose system which we call scholasticism.' 
Abu Ali Ibn Sina, the 'Avicenna' of Europe, who has been 
described as the Aristotle of the Arabians and certainly the most 
extraordinary man the nation produced, was not, in fact, an 
Arab but a Persian. He was born near Bukhara in A.D. 980, and 
his father was a native of Balkh. After the birth of Avicenna 's 
younger brother, the family moved into Bukhara itself, where 
a tutor was engaged to instruct the future philosopher in the 
Koran and in Arabic poetry. The boy's progress was so rapid 
that auxiliary teaching aids were soon required, and he was 
taught arithmetic by a greengrocer, law by an ascetic named 
Ibrahim, and Euclid and logic by a wandering scholar named 
Natili whom his father lodged in the house for his son's benefit. 
Natili seems to have had but a slender stock of knowledge, and 
Avicenna, having discovered this, applied himself with energy 
and resolution to a course of hard private study. Among many 
other subjects he studied medicine, * which', he says, 'is not 
difficult,' and by the age of 1 6 he had advanced so far that adult 
qualified physicians came to learn from him. From 16 to 17 he 
worked at philosophy, which he found very difficult. Every 
time he encountered a problem that was too troublesome for 
him, he would go to the mosque and spend the day in prayer, 
after which he returned to his house, lit the lamp, and set him- 
self once more to study. When he became sleepy, he would 
drink a glass of wine to stimulate his weary brain and apply 
himself to his books again. Even when at last he could remain 
awake no longer, he revolved his problems in his dreams and 
sometimes solved them in his sleep. 

yo Avicenna 

Appointed physician to one of the princes of the country at 
the tender age of 17, Avicenna held many important posts 
in after years, on one occasion being grand vizier or prime 
minister ; but he was too fond of the bodily pleasures of life and 
died comparatively young in 1036/7. During his brief life, 
however, he accomplished an amazing mass of literary, medical, 
philosophical and scientific work, and became an almost 
legendary hero to his fellow-religionists and even to medieval 

It is uncertain whether Avicenna ever wrote any books wholly 
devoted to chemistry. Several medieval Latin works on alchemy 
are known which profess to be translations from Arabic books of 
his, but for the most part their authenticity is open to grave doubt. 
Recently, however, it was discovered that a well-known Latin 
tractate on Minerals, sometimes ascribed to Geber, sometimes 
to Aristotle, and sometimes to Avicenna, is partly a direct transla- 
tion and partly a resume of sections of a genuine work of Avicenna , 
namely, the Book of the Remedy, which he composed in response 
to his friend Al-Juzjani's request that he should write a general 
commentary "on "Aristotle's works. He was too busy to write 
a formal commentary, but compromised by writing a plain ex- 
position of his own views free from any attempt at refutation of 
adverse opinions. He had already written the first book of his 
great Canon of Medicine, and thereafter worked at the Remedy 
and the Canon simultaneously. At this period he was living at 
Hamadhan under the protection of a prince named Shams al- 
Daula, who died in A.D. 1021, and whose vizier he was. After 
the death of Shams al-Daula, Avicenna secretly left Hamadhan 
and was honourably received at Ispahan by 'Ala al-Daula, who 
annexed Hamadhan in 1023 on the deposition of Shams al- 
Daula's son. It was during the time of his stay with 'Ala al- 
Daula that the Remedy was finished, and according to Ibn Abi 
Usaybi'a, a Muslim chronicler, the chapters which particularly 
interest us, namely those on Natural JScience, were composed 
after the death of Shams al-Daula in 1021, but before Avicenna 
went to Ispahan, probably in 1023 We are thus able to date them 

1 T CANT 1C A 

Cum carti^ 
Amhc.v AlnoiBcfluncnltshjI'ofolii.K rnc<iu 


'U* i rffrtt ijf'ptut wi<f <xtctjjt runt d> eoJem ft mul 

nottt* . 

Cumprnnlcgn 1 ? Pummt Pontinv-ts,Frani.omm 
cnaftis Vcnco. 

Fig. 21. TITLE-PAGE OF AVICENNA'S Canon of Medicine 

72 Avicenna 

very precisely. The Latin translation was made by Alfred the 
Englishman about A.D. 1200. 

The first part of the section on minerals deals with the forma- 
tion of rocks and stones and other geological phenomena, in the 
discussion of which Avicenna anticipates in a remarkable way 
the conclusions of Leonardo da Vinci and Nicholas Steno. The 
second part of the book consists of an account of the properties 
of minerals and metals, and is of very considerable interest 
and importance. Mineral substances, says Avicenna, may be 
roughly divided into four groups, namely, stones, fusible sub- 
stances, sulphurs and salts. The basis of this classification is that 
some of the mineral bodies are weak in substance and feeble in 
composition and union, while others are strong in substance. 
Of those which are feeble in substance, some have the nature of 
salt and are easily soluble in water, such as alum, vitriol and sal- 
ammoniac, while others are oily in nature and are not easily dis- 
solved by moisture alone, such as sulphur and realgar and 
orpiment. All malleable bodies are fusible, though sometimes 
only indirectly, whereas most non-malleable substances cannot 
be fused by ordinary methods or even softened except with 
difficulty. As regards the stony kinds of naturally occurring 
mineral substances, the material of which they are made is 
aqueous, but they have not been solidified by the action of cold 
alone. Their solidification has, on the contrary, been brought 
about by the action of dryness, which has converted the wateri- 
ness into earthiness. They do not contain a quick, oily humidity 
and so are non-malleable; and because their solidification has 
been caused mainly by dryness, the majority of them are in- 
fusible unless they are subjected to some physical process that 
facilitates fusion. 

Alum and sal-ammoniac belong to the family of salts, though 
sal-ammoniac possesses a fieriness in excess of its earthiness, and 
may therefore be completely sublimed. It consists of water 
combined with a hot smoke, very tenuous and excessively fiery, 
and has been solidified by dryness. In the case of the sulphurs, 
their wateriness has suffered a vigorous leavening with earthi- 

Avicenna 73 

ness and airiness under the action of heat, so far as to become 
oily in nature; subsequently it has been solidified by cold. 

The vitriols are composed of a salty principle, a sulphureous 
principle, and stone, and contain the virtue of some of the 
fusible bodies (that is, metals). Those of them which resemble 
yellow and green vitriol are formed from the crude mineral 
vitriols by partial solution, the salty constituent alone dissolving, 
together with whatever sulphureity there may be. Solidification 
follows, after a virtue has been acquired from a metallic ore. 
Those which acquire the virtue of iron become red or yellow, 
while those which acquire the virtue of copper become green or 

Mercury seems to be water with which a very tenuous and 
sulphureous earth has become so intimately mixed that no 
surface can be separated from it without something of that 
dryness covering it. Consequently it does not cling to the hand 
or confine itself closely to the shape of the vessel which contains 
it, but remains in no particular shape unless it is 'subdued'. 

On the constitution of metals, Avicenna follows Jabir very 
closely. He regards the proximate constituents to be mercury 
and sulphur, or bodies closely resembling them. If the mercury 
is pure, he says, and if it is commingled with the virtue of 
a white sulphur which neither induces combustion nor is impure, 
but on the contrary is more excellent than that prepared by the 
alchemists, then the product is silver. If the sulphur, besides 
being pure, is even better than that just described, and whiter, 
and if in addition it possesses a tinctorial, fiery, subtle and non- 
combustive virtue, it will solidify the mercury into gold. Then 
again, if the mercury is of good substance, but the sulphur 
that solidifies it is impure, possessing on the contrary a 
property of combustibility, the product will be copper. If the 
mercury is corrupt, unclean, lacking in cohesion and earthy, 
and the sulphur is also impure, the product will be iron. As for 
tin, it is probable that its mercury is good but that its sulphur is 
corrupt; and that the commingling of the two is not firm, but 
has taken place, so to speak, layer by layer, for which reason the 

74 Avicenna 

metal * shrieks'. This is, of course, a reference to, and an 
attempted explanation of, the well-known 'cry of tin', which 
modern chemistry ascribes to friction of the crystalline particles. 
Lead, says Avicenna, is probably formed from an impure, fetid, 
and feeble sulphur, for which reason its solidification has not 
been thorough. 

Avicenna then proceeds to demolish the alchemists. There is 
little doubt, he says, that the alchemists can contrive to make 
solids in which the qualities of the metals are perceptible to the 
senses, though the alchemical qualities are not identical in 
principle or in perfection with the natural ones, but merely bear 
a resemblance and relationship to them. As to the claims at 
transmutation made by the alchemists, it must be clearly under- 
stood that it is not in their power to bring about any true change 
of the metallic species. They can, however, produce excellent 
imitations, dyeing a red metal white so that it closely resembles 
silver, or dyeing it yellow so that it closely resembles gold. They 
can, too, dye a white metal in such a way as to make it resemble 
gold or copper, and they can free lead and tin from most of their 
defects and impurities. Yet in these dyed metals the essential 
nature remains unchanged ; they are merely so dominated by 
induced qualities that errors may be made concerning their real 
nature. 'I do not deny', he proceeds, 'that such a degree of 
accuracy in imitation may be reached as to deceive even the 
shrewdest, but the possibility of transmutation has never been 
clear to me. On the contrary, I regard it as impossible, since 
there is no way of splitting up one metallic combination into 
another. Those properties that are perceived by the senses 
are probably not the differences which distinguish one metallic 
species from another, but rather accidents or consequences, the 
essential specific differences being unknown. And if a thing is 
unknown, how is it possible for any one to endeavour to pro- 
duce it or to destroy it ?' It is, indeed, quite clear that Avicenna 
was contemptuous of the pretensions of alchemy, for he winds 
up by remarking that there was much he might have said on the 
subject, but that it would probably have been a sheer waste of 

Avicenna 75 

time a remark which the Latin translator tactfully omitted 
from his version. 

As may easily be imagined, scepticism concerning alleged 
transmutation had long existed. Some denied the possibility 
altogether; others agreed that transmutation might be effected, 
but only by magic. Al-Jildaki (p. 81) tells us that in Jabir's time 
disbelief in alchemy was very pronounced, while the great Razi 
was forced to write a book to confound the sceptics, among 
whom was the celebrated Christian scholar and translator Hunain 
ibn Ishaq. Avicenna's attack did not go unanswered. His argu- 
ments were examined carefully by the vizier Al-Tughra'i, better 
known as a skilful poet, and were shown to be inconsistent with 
views that Avicenna had himself expressed in other passages in 
the same book, and so the controversy went on. It is, indeed, not 
unreasonable to maintain that the theory of the possibility of 
transmutation was in better accord with observed facts and with 
the general philosophic scheme of the time, than the contrary 
thesis so vigorously upheld by Avicenna ; and that it was there- 
fore temporarily true, in the pragmatic sense. In any case, the 
time was not yet ripe, and alchemy was to hold sway for several 
centuries to come. 

It is not surprising that honest attempts at transmutation 
were often brought under suspicion by the knavish tricks which 
charlatans employed to deceive the innocent. In the popular 
literature, the alchemist is always, or almost always, a rogue, as 
in the following typical anecdote : 

A Persian charlatan [says Carra de Vaux] , having arrived at Damas- 
cus, took 1,000 dinars of good Egyptian gold, filed them up and 
mixed the filings with charcoal, various drugs and ordinary flour. 
To this mixture he added fish-glue, made the whole into a paste, 
and moulded the latter into small pellets which he allowed to dry. 
He then clothed himself in the habit of a darwish, and, taking the 
pellets to a druggist sold them for a few dirhams under the name of 
Tabarmaq of Khurasan. After which, having assumed a rich 
cloak, he engaged a slave and went to the mosque, where he 
scraped acquaintance with several notable persons. He told them 

76 Avicenna 

that he was an expert in alchemical science, able to make untold 
wealth in a single day. The vizier, hearing of this alchemist, 
ordered him to attend and presented him to the Sultan, who ex- 
pressed his desire to witness a transmutation. The charlatan 
produced a recipe in which, among a large variety of drugs, 
Tabarmaq of Khurasan was indicated, to the extent of 100 mith- 
qals. All the rest of the drugs were easily obtained, but at first no 
trace of Tabarmaq could be discovered. The man insisted upon 
its necessity, however, and when the druggists' shops had been well 
searched the discovery was at length made of course in the shop 
of the druggist to whom the Tabarmaq had been sold a few days 
previously, and who stated that he had obtained it from a darwish. 
The pellets were bought, and the Persian ordered the ingredients 
to be placed in a crucible and strongly heated. When all was 
sufficiently hot: 'Take out the crucible/ he said. It was taken out 
and turned upside down, when a fine ingot of gold rolled out. 

The Sultan, struck with amazement, ordered the Persian to be 
rewarded. It was now merely a question of finding more Tabarmaq. 
Search failed to reveal any more in Damascus. 'I know a cavern', 
said the charlatan, 'in a certain mountain in Khurasan, where a 
large quantity is to be found. Send some one to dig it out and bring 
back a thousand camel-loads.' 'Go thyself, said the Sultan. The 
man, after judicious reluctance, allowed himself to be persuaded, 
and accepted the mission. He was furnished with everything 
needful for the journey : a tent, a travelling kitchen, sugar, carpets, 
stuffs and silks, manufactured objects from Alexandria, and, in 
addition, a large sum of money. Thus equipped, he set out and 
as might have been expected that was the last that was seen of 

In spite of the efforts of Avicenna, belief in the existence of 
the Elixir continued, and chemistry became more and more 
speculative and more widely divorced from experimental fact. 
Such men as Ibn Arfa Ra's (twelfth century), whose alchemical 
poem called The Particles of Gold enjoyed the highest reputa- 
tion among later Muslim adepts, more closely resemble Thomas 
Norton and Philalethes than van Helmont : they were mystical 
alchemists rather than practical craftsmen, and the interest of 
their writings is for the occultist rather than the historian of 

The ' Sage's Step'. 77 

scientific chemistry. There are, however, a few notable ex- 
ceptions. Mansur al-Kamily, chief chemist at the Egyptian 
Mint at Cairo in the thirteenth century, wrote a practical hand- 
book on the extraction, purification and assaying of gold, com- 
pletely free from the usual alchemical verbosity and theorizing. 
It is extremely rare ; there is, indeed, only one copy in existence, 
which is preserved in the Library of the King of Egypt. The 
contents of the book show that Arab chemists of the thirteenth 
century were well acquainted with cupellation, the parting of 
^old and silver by means of nitric acid, the extraction of silver by 
amalgamation with mercury, and with the quantitative chemical 
analysis of gold/silver alloys. The Probierbuechlein and Agri- 
cola's De Re Metallica, of the middle of the sixteenth century, 
contain scarcely any improvements upon the methods described 
by Mansur al-Kamily. 

23. The 'Sage's Step' 

CONTEMPORARY with, or slightly later than, Avicenna was the 
author of a remarkable book entitled The Sage's Step, which is 
said to have been composed in 1047-50. For long this book was 
thought to have been written by Maslama of Madrid, the most 
brilliant of a brilliant group of Spanish Arabs who flourished 
ander the Caliph Al-Hakam II (A.D. 961-76). He was the chief 
Tnathematician and astronomer of his time, and the lustre of his 
lame was increased by his skill in the science of the division of 
nheritances. Born at Cordova, he was educated partly in the 
Drient, and while there seems to have come into contact with the 
:elebrated Encyclopaedists of Islam, the 'Brethren of Purity', 
kvhose 'Letters' (which cover a wide range of contemporary 
cnowledge) he is believed to have brought back with him to 
Europe in a new recension. His authorship of The Sage's Step, 
lowever, is very doubtful, as he died about A.D. 1007, and in any 
:ase before the outbreak of the civil war in Spain (1009), while 
he author of the book plainly states that he composed it on account 
)f the lamentable state into which scientific learning had fallen 
ince the civil war had spread its ravages throughout the land. 

78 The 'Sage's Step 5 

The writer, whoever he was, was no armchair chemist but 
a man who knew the discipline of the laboratory. Chemistry was 
to him a noble science exacting the most a man could give. 
Before beginning to study it, the aspirant should undergo a 
thorough mathematical training by reading Euclid and the 
Almagest of Ptolemy, and should then proceed to the De Caelo 
et Mundo, De Generatione et Corruptione, Meteor ologica, and 
Physica Auscultatio of Aristotle, or, failing these, the Canon of 
Apollonius of Tyana. Having thus acquired a knowledge of the 
main theories of natural science, the chemist should practise his 
hand in operation, his eye in examination, and his mind in 
reflection over chemical substances and reactions. Since 
Nature's behaviour is invariable, for she never does the same 
thing in different ways, the chemist must strive to follow Nature, 
whose servant indeed he is, like the physician. The latter 
diagnoses the disease and administers a remedy, but it is Nature 
that acts. 

In general, the theory of the author of The Sage's Step does not 
show any marked advance upon that of Jabir and Razi, whom 
he often acknowledges to be his masters (for Jabir, in fact, he 
expresses unbounded admiration), but the book serves to show 
the progress which had been made in experimental methods and 
in empirical knowledge during the hundred and fifty years 
or so that had elapsed. One observation is of particular 
interest to chemists as in it occurs the first definite description of 
a substance which was destined, in the hands of Priestley and 
Lavoisier, to play an historic role mercuric oxide: 'I took 
natural quivering mercury, free from impurity, and placed it in 
a glass vessel shaped like an egg. This I put inside another vessel 
like a cooking-pot, and set the whole apparatus over an extremely 
gentle fire. The outer pot was tfyen in such a degree of heat that 
I could bear my hand upon it. * I heated the apparatus day and 
night for forty days, after which I opened it. I found that the 
mercury (the original weight of which was Jib.) had been com- 
pletely converted into a red powder, soft to the touch, the weight 
remaining as it was originally/ 

The 'Sage's Step' 79 

That no gain in weight was observed is not surprising, as some 
of the mercury would probably have been lost by volatilization, 
while the increase in weight of mercury on oxidation is only 
about 8 per cent. The fact, however, that the author attempted 
to carry out the experiment quantitatively is in itself important, 
as indicating that he paid attention to a fundamental chemical 
rule not universally observed until centuries later. 

The author's remarks upon Jabir (whom he states to have 
lived some 150 years earlier) are worthy of mention. Jabir, he 
says, struck out a new line and cut himself off from the old 
tradition. He found that most people were sceptical of the 
possibility of obtaining the elixir, while those who did believe 
were of the most ignorant type. He therefore decided to give 
instructions of a more practical kind, and thus improved upon 
Khalid ; the latter wrote in an obscure style and wished merely 
to show men that he himself was accomplished in alchemy, 
whereas Jabir wished to help and instruct others. The great 
value of Jabir's works, he continues, lies in this very fact of their 
being practical, for if a man reads of a process first and then 
carries it out in practice, he will naturally believe in the truth of 
the Art. As a matter of fact, all the various operations that 
Jabir describes, such as calcination, are in reality transmutations 
of one substance into another, so that by performing them the 
sceptic may gradually be led to belief. The theory of the Art is, 
indeed, difficult, but its practice is easy. 

The author then turns to a consideration of sulphur, mercury, 
marcasite, tutia, magnesia, talc, lazward, vitriols, alums and 
other necessary substances, afterwards giving an account of 
the purification of gold and silver, the chief points of which are 
as follows : 

Silver alloyed with lead may, be separated from the latter by 
placing it in a cupel made from bones (called the * dog's head' or 
commonly the kuraja ; it is a crucible made from burnt bones) 
and fusing it by means of a strong fire. The lead is removed and 
absorbed by the cupel and the silver is left pure and free from 
base metal. Silver may be separated from copper in the cupel by 

8o The 'Sage's Step' 

the continual addition of lead ; after a time the silver appears in 
a state of purity. 

Gold may be purified from silver and copper in two ways. 
From copper alone it may be refined by the method used to 
purify silver from copper, namely, cupellation with addition of 
lead. If it is so desired, sulphur may be added as well ; this burns 
the copper and the gold remains pure. Gold may be purified 
from lead by the method used to refine silver from lead. 

The purification of gold from silver may be carried out in two 
ways, one by means of 'stones' and the other by means of salts. 
The former method is as follows : the gold alloyed with silver is 
beaten out into thin leaves and these are placed on a bed of 
haematite and salt and covered with more of the same mixture 
followed by a layer of red clay. The whole is then heated in the 
oven known to men of science as the 'refining-furnace', when the 
silver is absorbed by the earthy matter and the gold leaves are 
left pure, containing nothing but the most refined gold. 

This operation may also be carried out in a similar way by 
using alum and salt or by means of old baked clay. The clay is 
finely powdered and mixed with an equal amount of salt and the 
two well powdered again. The mixture is then spread in a layer 
on a layer of red clay. A gold leaf is next added, followed by 
another layer of the mixture of clay and salt, and so on until all 
the gold has been added. A covering layer of clay and sand is 
then placed on the top and the whole strongly heated, when the 
gold is purified and extracted from the silver. The silver may 
be recovered merely by the addition of mercury to the earthy 
residue. The mercury thickens and coagulates until it becomes 
like dough. At this stage it is placed in a crucible over the fire 
and the mercury then volatilizes away, leaving the silver. 

Gold may also be separated from silver in the same way that it 
is separated from copper. The gold-silver alloy is mixed with 
a little copper and the mixture fused, with the addition of red 
sulphur from time to time. The silver burns away from the gold 
and the latter is left pure. The former method, however, is the 
more efficient. 

Later Writers 81 

In the Letters of the Brethren of Purity the Jabirian sulphur- 
mercury theory of the constitution of metals is adopted, com- 
bined, however, with an astrological theory. There is also an 
insistence upon the Aristotelian 'four qualities', and the com- 
position of minerals and precious stones is stated in terms of 
these qualities with a naive dogmatism. 

24. Later Writers 

No account of chemistry in Islam would be even approximately 
complete which omitted to mention Abu'l-Qasim of Iraq and 
Aidamir al-Jildaki. The first of these men lived in the thirteenth 
century, probably at Cairo, and has left us several books which, 
apart from their intrinsic interest, serve to indicate the trend of 
alchemical thought and practice in Islam after the process of 
transmission to Europe (see pp. 84-106) had been in action for 
some considerable time. It is very obvious that in Abu'l- 
Qasim's time the reaction of European scientific thought upon 
Islam had not yet begun, and the contrast between the two 
intellectual worlds could not be better exemplified than in the 
persons of Abu'l-Qasim and his contemporary Roger Bacon 
(p. 92). The driving force of Islam was beginning to grow weak, 
while the new stimulus that Arabic learning had given to 
Europe had resulted in a scientific renaissance which was to 
reach its full development not long afterwards. Abu'l-Qasim 's 
outlook is that of his predecessors of three or four centuries 
earlier, and although there was unquestionably some advance in 
empirical practical chemistry, the theoretical views expressed 
are supported by quotations not merely from Jabir but from the 
still earlier alchemists of the Alexandrian school. Abu'l-Qasim 
himself seems to have been a good experimentalist and a com- 
paratively logical thinker, but his general views often represent 
a retrograde movement upon those of Jabir. 

Aidamir al-Jildaki, who also lived for part of his life at Cairo, 
is of importance chiefly on account of his extensive and deep 
knowledge of Muslim chemical literature. He apparently spent 
the major portion of his existence in collecting and explaining 

2613-4 O 

82 General Review of Muslim Chemistry 

all the books upon alchemy that he could discover, and his 
labours are now beginning to receive their reward; for his 
writings form an indispensable source of a great deal of our 
knowledge of chemistry and chemists in Islam . In a few instances 
it is possible to observe that he must have carried out experi- 
mental work himself, but for the most part his books are com- 
mentaries upon the works of earlier writers. Thus his great 
End of the Search is a commentary upon Abu'l-Qasim's Book of 
Knowledge Acquired concerning the Cultivation of Gold, and 
although his explanations are not seldom more obscure than the 
passages they are designed to illuminate, he had the admirable 
habit of making innumerable and lengthy quotations from 
Khalid, Jabir, Razi and many other authors, and his books are 
thus a rich storehouse of information upon Muslim chemistry. 
It is therefore necessary to inquire into the question whether his 
quotations and historical facts are authentic, and whether his 
reliability is to be accepted or doubted. Fortunately, it often 
happens that a book from which he quotes is extant, and his 
quotations in such cases can of course be checked. A test con- 
ducted on these lines has shown that Jildaki was conscientious, 
and although he does not always come through unscathed, his 
general trustworthiness can be safely assumed. He thus 
deserves the warmest thanks of all who are interested in the 
history of chemistry. 

25. General Review of Muslim Chemistry 

BEFORE passing on to the next period of the development of the 
science, it will be useful to review the salient features shown by 
the chemistry. of Islam; for we shall then the better be able to 
appreciate both its defects and its merits. And since, as we shall 
shortly find, early European chemistry is almost wholly a legacy 
from Islam, it is impossible to understand medieval Latin 
alchemy without a clear idea of the work of the Arabs. 

Until the time of Jabir, chemistry was 'without form and void'. 
The solid technical knowledge of the craftsmen was lost in the 
vapourings of occultists, and if there were any men with a more 

General Review of Muslim Chemistry 83 

reasonable view of chemical science, its aims, its objects and its 
methods, we find no record of them. By the efforts of Jabir and 
Razi, the two Muslim chemical geniuses, much of the vast 
accretion of unbridled speculation was cleared away, and 
chemistry first began to take shape as a true science. Experi- 
mental fact was at last informed with the beginnings of reason- 
able theory, while on the practical side a workmanlike scheme of 
classification was evolved and a wide range of substances was 
carefully investigated and systematically characterized. The 
common laboratory methods of distillation, sublimation, cal- 
cination, reduction, solution and crystallization were improved 
and their general purposes well understood. The refinement of 
metals, by cupellation and in other ways, was brought to a high 
degree of perfection, and the careful assay of gold and silver was 
accompanied by extraordinary accuracy in methods of weighing 
and in the determination of specific gravities. 

On the theoretical side, the idea that 'base' metals could be 
transmuted into gold or silver overshadowed every other. The 
generally accepted belief was that elixirs could be prepared 
which, by an action we should now describe as catalytic, would 
convert practically unlimited amounts of lead, mercury, tin, 
copper, or even iron into silver first and then into gold. There 
were alternative theories as to the means whereby transmutation 
could be effected, but as we may more conveniently study these 
in their later developments a mere reference to them in passing 
may be sufficient at the moment. The philosophical justification 
for the almost universal credence in the possibility of trans- 
mutation is to be found ultimately in the Aristotelian conception 
of the Four Elements and proximately in Jabir J s theory that all 
metals are composed of sulphur and mercury. Its practical 
justification lay in the elegant manner in which it explained 
numerous phenomena and stimulated unceasing research. 

As with all other branches of natural science, alchemy was 
often permeated with magical and astrological superstitions, 
particularly in the later years of the period. The rationalistic 
temper of Razi and Avicenna had not completely extirpated 


84 The Translators 

the weeds of occultism, and unfortunately Jabir, the hero of 
Muslim chemists, had so frequently allowed his mystical reflec- 
tions to colour his chemical writings that his books afforded 
excellent material for those who practised alchemy as an esoteric 
cult rather than as a reasonable branch of the philosophy of 
Nature. Yet, on the whole, the scientists of Islam were the first 
to apply scientific methods to the study of chemical phenomena ; 
and the tongue of the infant science of chemistry is that of the 

26. The Translators 

WHILE medieval Europe was, of course, by no means destitute 
of skilful dyers, painters, glass-makers, practical metallurgists, 
and other craftsmen, there seems to be no doubt that chemistry 
as a science was a definite importation from the civilization of 
Islam. The role which Islam played as the transmitter of Greek 
learning to late medieval Christendom is so well known that it 
need not be emphasized here; but its particular importance in 
the history of science, especially chemistry, has not always been 
fully realized. As Professor C. H. Haskins has recently reminded 
us, practically the only contact between Islam and Christian 
Europe until the twelfth century was through the Crusades, 
which were clearly not favourable to the transmission of learning. 
Soon after A.D. noo, however, European scholars began to dis- 
cover that the Saracens were possessed of much knowledge and 
ancient wisdom, and the bolder spirits began to travel in Muslim 
lands in search of learning and enlightenment. Sicily, an 
appanage of Islam from 902-1091, was taken by the Normans 
in the latter year, but Muslim physicians and other scientists 
were retained at the Norman court, and the island thus became 
a centre of diffusion of Arabian learning. It was, however, in 
Spain that the greatest activity prevailed. Christian students 
were welcomed to the Muslim colleges and libraries at Pamplona^ 
Segovia, Barcelona, Toledo and other Spanish towns, and study 
was soon followed by translation. 

Some of the chief translators were Adelard of Bath, Gerard of 


86 Robert of Chester 

Cremona, Robert of Chester, Alfred the Englishman, Plato of 
Tivoli and Hermann of Carinthia : men diverse in nationality 
and taste but alike in their passionate desire to open the treasuries 
of Saracen knowledge to Latin Christianity. Besides original 
Arabic treatises, many Greek works thus became available to 
medieval Europe for the first time, together with commentaries 
and expositions which did much to direct the future progress of 
European thought. 

This is not all: with the Arabs^and Jews of the Middle Ages, 
scientific knowledge was a thing of supreme importance, and this 
spirit of devotion to science passed to the Latins who came in 
contact with their learning. With interest came method: a ration- 
alistic habit of mind and an experimental temper. These, of course, 
could have been found among the ancient Greeks and were in- 
herent in their writings, but they had been fostered and kept alive 
in the Mohammedan countries, and it was chiefly from these that 
they passed to Western Christendom. 1 

27. Robert of Chester 

ON ii February in the year 1144 the Englishman, Robert of 
Chester, finished the first translation from the Arabic of a book 
on chemistry, the Book of the Composition of Alchemy. In the 
preface to his translation he says, * Since what Alchymia is, and 
what its composition is, your Latin world does not yet know, 
I will explain in the present book/ If this story is to be believed 
but there is some reason to suspect it the introduction of 
chemistry into Europe is an honour of our native land ; so no 
English history of chemistry can dismiss Robert of Chester with 
a mere word in passing. 

Of Robert's early life we know nothing beyond the facts that 
he may have been a native of Ketton in Rutland and that he was 
doubtless educated in the well-known school at Chester. In 
1141, he and his friend Hermann the Dalmatian were living in 
Spain near the Ebro, studying the arts of astrology. In that 
year Peter the Venerable found them and persuaded them to 
translate the Koran, a task which they finished in 1143. Robert 

1 C. H. Haskins, The Renaissance of the Twelfth Century, London, 1928. 

Robert of Chester 87 

must then have returned to his beloved sciences, for the Com- 
position of Alchemy, as we have seen, was finished early in the 
following year. For some time, Robert was Archdeacon of 

Jit tm mcfcro^ 
tvim >*i^[m Tii 


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tru pun te 

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-Oinr in 

ftrwiK furfih ftair pfirt 

no qut ftjir >tnnim Imottcib; 

cjtu tanrond 
<rc ctti tftr tuKMw tn 
i ojjc wtUan n- G 
dntrr niqircrv ab ontniV; in 

' aim qmftrum I 

^u r r ii tMli^ ><T0D if o* 
nb: n^mmiinf finn ? titni ab 
tc otni TV ^ ^fti wlr jjanfrci'i* 
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rojcrn anrj re till tyt m* Utii 
trn* 0>rtr dr Pdlib <*C" 
tirtm ^ tftn r^< -*4r >JIc W 1N 
in *i mttif .^ 01 ti 

oput nuifof nuucufttf -i ego 
tv (ow ftteutm her aim tjUt* quo 
ffn ci tern q in dfr Jxrtn IM m tncniw; 
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D fir 7 nur utin Im ivgnom 1 rfr Tuu^ 

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tti !* re tu^mi 

tmtif te todb UmK cfntrt 

nialnm fiiwntm- 
ftyfiipg- vl Ty> illc ]dm ttilj" ftf* 
(c''i tint* hie pfcumh CiuiiCiic^dW 
full tnuTf f~diil> -V tulfir ttrtnAg-" 

FiJjt tJiotxvl" ^nipTtuulfptriilit* o-'STtnif uit 

' grfifc (i uif fi r txpc tMUl> ur mm mlnf ftlr 

w ntticn HW 
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^.'? tutlm > 

ajiw^.'? r 

Pampeluna, in northern Spain, but he returned to London in 
1 147 and again in 1 150. In addition to his services to chemistry, 
Robert translated the Algebra of the celebrated Muslim mathe- 
matician Al-Khwarizmi and thus introduced into Latin Europe 

88 Robert of Chester 

both a new science and a new branch of mathematics. He also 
calculated a set of astronomical tables for the meridian of London 
(1149/50) and wrote a treatise on the astrolabe (London, 1147).' 
Robert's pioneer work was followed by many other transla- 
tions in rapid succession. By the middle of the thirteenth 
century, in spite of some ecclesiastical opposition (which was, 
however, much less than has sometimes been asserted), there 
was a vigorous scientific renaissance, and the chief books of the 
Muslim chemists and of Aristotle and other Greek philosophers 
had been translated from the Arabic and diligently studied. 
Our knowledge of this transition period is, however, unfortu- 
nately inadequate, in spite of the fact that there is abundant 
material available for study. When the manuscripts preserved 
in our libraries, and recently catalogued for us in a most admir- 
able way by (Mrs.) Dorothea Waley Singer, are systematically 
examined, much that is now difficult and obscure will become 
clear. There can be no doubt that many Latin works which 
profess to be translations from the Arabic are spurious, written 
by Europeans and fathered upon the great names of Greek and 
Islamic chemistry. Nevertheless, recent research has shown 
that among the mass of extant Arabic manuscripts are several 
that appear to be originals of works hitherto known only in 
Latin dress, and further investigation would doubtless reveal 
many more similar cases. It seems, therefore, that we should not 
be too hasty in dismissing as falsifications early Latin works 
which profess to be translations from the Arabic ; in any event 
there can be no doubt that the translations which were made in 
the twelfth and thirteenth centuries by men like Robert of 
Chester, Hermann of Carinthia, Gerard of Cremona and 
Adelard of Bath formed the foundation upon which European 
chemistry was built. 

At first, progress in the new subject was slow (though by 1350 
a monk of Bologna possessed no fewer than 72 alchemical works), 
and the books of the period are, at bottom, little more than 
compilations of excerpts from earlier writers. The galaxy of 
brilliant men who busied themselves with science in the 

Vincent de Beauvais 89 

thirteenth century, men whose names are familiar to students of 
the Middle Ages Vincent de Beauvais (c. 1190-1264), Albertus 
Magnus (1193-1282), Roger Bacon (1214-1292), Raymond 
Lully (1225 or 1235-1315), and Arnold of Villanova (1240-1313) 

Ptg. 24. 

made little real advance in chemistry, as we shall see by taking 
a glance at their works. 

28. Vincent de Beauvais 

VINCENT DE BEAUVAIS, a Dominican monk, for some years 
'reader' in the Cistercian monastery at Royaumont, and tutor tfe 
the two sons of Louis IX, divides minerals into four classes: 

90 Albertus Magnus and Roger Bacon 

metals, stones, sulphureous bodies, and salts. Each metal is 
considered separately, and appropriate quotations are made 
from Razi, Avicenna and others. The generation of metals is 
considered, and Avicenna 's doubts as to the possibility of 
transmutation are reproduced. Finally, a good deal of material 
of a practical nature is included. Vincent de Beauvais notices the 
theory that metals are composed of sulphur and mercury, which, 
as we have seen, was first clearly stated by Jabir, and expresses 
his firm belief that 'by the art of chemistry mineral bodies, 
especially metals, may be transmuted from their own species 
into others'. 

29. Albertus Magnus and Roger Bacon 

ALBERTUS MAGNUS, Count of Bollstadt, was born at Lauingen 
in Suabia, probably in the year 1193, though some say 1206. 
Joining the Dominican Order at Padua in 1223 he rapidly 
became a miracle of learning and was popularly known as 
the Doctor Universalis though his detractors contemptuously 
nicknamed him 'the Ape of Aristotle'. From 1228 to 1245 he 
taught in Cologne and other German cities, while from 1245 to 
1248 he lectured in Paris and began the publication of his great 
philosophical encyclopaedia. From 1254 to 1262 he occupied 
important ecclesiastical offices in Germany, but in the latter 
year he retired to a cloister at Cologne to spend the remainder 
of his life in study. He is said to have died at Cologne on 
1 5 November 1280. A genuinely pious man, he conformed strictly 
to the rules of his order, even walking barefoot on his official 
journeys through the parts of Germany under his supervision. 
His fame as a teacher was so great that the young Thomas 
Aquinas made the long journey from Italy to Cologne to become 
his pupil. 

Albertus whom tradition describes as a man of exceedingly 
small stature was a widely-read scholar, and although his 
reputation rests mainly upon his philosophical works, he had an 
extensive and unusually accurate knowledge of contemporary 
science, which he describes in his Book on Minerals and else- 

Albertus Magnus and Roger Bacon 91 

where. Although he yielded to none in his admiration of 
Aristotle, he would not agree that the great philosopher was 
either infallible or omniscient, and held that the development 
of science was not closed by his death. Albertus felt a keen 
'desire for concrete, specific, detailed, accurate knowledge con- 
cerning everything in nature ', and maintained that, in the study 
of natural phenomena, one should not merely transcribe an 
ancient statement but observe with his own eyes and mind. Yet 
he does not appear to have appreciated the extreme scientific 
importance of experiment, as distinct from observation, and 
though he tested the genuineness of alchemical gold, and offered 
bits of iron to ostriches to ascertain whether the old story was 
true, these were exceptional cases and find few parallels in his 
writings. Like all his contemporaries, he believed in magic and 
astrology, and, in spite of his own canon of criticism, is often 
quite ready to admit the fabulous. 

Albertus was not an Arabic scholar, but was well acquainted 
with Latin translations of Avicenna, Averroes and other Muslim 
writers. In his De Miner alibus he moulds his views upon 
alchemy very largely in accordance with Avicenna's opinions 
expressed in the chapters from The Remedy translated about 
1 200 by Alfred the Englishman. Thus he believes that most 
alchemists merely succeed in dyeing metals so that they resemble 
gold or silver, the actual metallic species remaining unaltered. 
'Alchemy', he says, 'cannot change species but only imitate 
them. ... I myself have tested alchemical gold and found that 
after six or seven ignitions it was converted into powder/ 
Perhaps, however, in this passage of his Miner alia he is referring 
only to the generality of the alchemists, for in another book, 
entitled Libellus de Alchimia, he relates that he was given a 
knowledge of alchemy by the grace of God. It is true that the 
authenticity of the Libellus is not definitely established, but it 
was ascribed to Albertus before 1350. The author recounts the 
errors of his predecessors, and promises to describe nothing but 
what he has actually seen. Next he states eight rules to be 
observed by the alchemist, much in the style of an admonition 

92 Albertus Magnus and Roger Bacon 

made five centuries earlier by Jabir. He then proceeds to discuss 
the various operations and pieces of apparatus employed in 
chemistry, and describes the common chemical substances and 
experiments that may be carried out with them. Finally, 
recipes are given for the production of gold and silver. The 
belief is expressed 'that metals can be produced by alchemy 
which are the equal of natural metals in almost all their qualities 
and effects ', except that alchemical iron does not possess magnetic 
properties and that alchemical gold lacks certain curative powers 
supposed to inhere in the natural metal. 

In general, Albert's chemical theory and practice show no 
advance upon Arabic knowledge of the ninth and tenth centuries. 
Avicenna's scepticism influences him at one time, while at 
another he seems to accept every alchemical commonplace. 
His undoubted zeal for an observational basis for the investiga- 
tion of natural phenomena was not entirely successful in 
emancipating him from belief in the occult, and in this respect 
he is typical of many minds of the thirteenth century. He 
nevertheless did much to popularize the study of science, and 
his influence was at least as great as that of the Doctor Admira- 
bilis, Roger Bacon. 

Roger Bacon, so far as our records go, was the first English- 
man, after Robert of Chester, to interest himself in chemistry. 
He was born at Ilchester in Somerset, probably in 1214, and 
' appears to have belonged to a wealthy family, which, sub- 
sequently, in the struggle between Henry III and the Barons 
(1258-65), sacrificed their fortunes in the cause of the King'. 
Bacon went to Oxford at an early age and took his M.A. degree 
some years later. Under the influence of the celebrated Grosse- 
tete he undertook the study of Greek, and it was doubtless 
Grossetete who persuaded him to join the Franciscan Order 
about 1247. From 1234-50 he studied and lectured at the 
University of Paris, choosing as his master 'one of the most 
modest and most learned men of the time, one who had devoted 
himself to the study of chemistry and mathematics and astro- 
nomy, and, above all, to those practical applications of experi- 

Albertus Magnus and Roger Bacon 93 

mental science which prompted his enthusiastic pupil to call him 
"the Master of Experiments" ', to wit, Petrus Peregrinus of 
Maricourt, the author of one of the first treatises on the Magnet. 
Between 1250 and 1257 h e probably spent most of his time at 
Oxford, but in the latter year, having fallen under the suspicions 


of the authorities of the Franciscan Order, he was sent to Paris 
and kept under a close watch until 1267. In 1268, probably 
owing to Papal intervention, he was permitted to return to 
Oxford; but his criticism of authority and independence of 
thought once again brought him into conflict with his superiors 
in the Order, and it is generally supposed that he was imprisoned 
again at Paris for fourteen years (1277-91). In 1292, once 
more at liberty, he returned to Oxford; but his freedom was 
short-lived, for 'the noble doctor Roger Bacon was buried at 
the Grey Friars [church of the Franciscans, long demolished], 
in Oxford, A.D. 1292, on the Feast of St. Barnabas the Apostle' 
[June 1 1] . A tower, traditionally known as 'Friar Bacon's Study', 
stood until 1779 on Folly Bridge, on the south side of Oxford. 

94 Albertus Magnus and Roger Bacon 

In 1267, Bacon writes, in his Opus Tertium, 

I have laboured from my youth in the sciences and languages, and 
for the furtherance of study, getting together much that is useful. 
I sought the friendship of all wise men among the Latins, and 
caused youth to be instructed in languages and geometric figures, 
in numbers and tables and instruments, and many needful matters. 
I examined everything useful to the purpose, and I know how to 
proceed, and with what means, and what are the impediments: 
but I cannot go on for lack of the necessary funds. Through the 
twenty years in which I laboured specially in the study of wisdom, 
careless of the crowd's opinion, I spent more than two thousand 
livres [about 10,000] in these pursuits on occult books (libros 
secretos) and various experiments, and languages and instruments, 
and tables and other things. 

Bacon was, indeed, 'a devotee of tangible knowledge', and 
emphasized the fundamental importance of experience and ex- 
periment in reaching the truth. His exact position in the history 
of science is, however, difficult to determine; and we may be 
sure that the tendency, observable in some quarters, to regard 
him as a lone figure, heralding the dawn of modern science amid 
the gloom of the thirteenth century, is very much to be depre- 
cated. It is clear that such a large question lies outside the scope 
of the present book, in which we need merely to ascertain 
Bacon's services, if any, to the progress of chemistry. For this 
purpose we must first obtain a rough idea of his general intel- 
lectual outlook. 

In the first place, Bacon in common with all other Christians 
of his age believed that the Bible contained, either explicitly or 
implicitly, the whole realm of knowledge. On the other hand, 
to understand the Bible thoroughly every art and science is 
necessary though the patriarchs and prophets had full know- 
ledge of all sciences, magic and astrology included. The queen 
of sciences is, therefore, Theology, and all other branches of 
learning are her handmaids. Round this central theme Bacon's 
whole system often very tactlessly expressed continually re- 
volves, and we cannot properly understand his attitude towards 


96 Albertus Magnus and Roger Bacon 

natural science if we forget this cardinal fact. His advocacy of 
the experimental method 'nothing can be certainly known but 
by experience' was therefore primarily concerned not with the 
search for objective truth, but with the exposition of scriptural 
scientific knowledge, and it is only within these limits that it 
must be envisaged. Bacon, in short, must be judged against the 
intellectual background of his day, and must not be gratuitously 
endowed with a mental outlook that, in actual fact, arose only 
very much later. Moreover, by experience, Bacon meant more 
than mere observation and experiment; for him, 'experience' 
included the illumination of faith, spiritual intuition and divine 
inspiration, and this esoteric experience was 'much better' than 
the 'experience of philosophy' or science. 

' Bacon's view of natural science was thus very different from 
our own. Yet, if we discount his broad philosophy and confine 
ourselves to his more detailed opinions on the advance of positive 
knowledge, we shall find that he always endeavoured to live up 
to his famous adage: sine experientia nihil sufficienter sciripotest. 
He applied this canon to all branches of science, including 
alchemy, of which he distinguished two kinds, viz. 'speculative' 
and 'practical'. Practical alchemy he regarded as more impor- 
tant than the other sciences, as more productive of material 
advantages than they. Speculative alchemy 1 
treats of the generation of things from the elements and of all 
inanimate things and of simple and composite humours, of 
common stones, gems, marbles, of gold and other metals, of 
sulphurs and salts and pigments, of lapis lazuli and minium and 
other colours, of oils and burning bitumens and other things with- 
out limit, concerning which we have nothing in the books of 
Aristotle. Nor do the natural philosophers know of these, nor the 
whole assembly of Latin writers. And because this science is not 
known to the generality of students it necessarily follows that they 
are ignorant of all that depends upon it concerning natural things, 
namely of the generation of animate things, of plants, and animals 
and men, for being ignorant of what comes before they are 
necessarily ignorant of what follows. . . . 

1 Stillman, The Story of Early Chemistry, London, 1924. 

Albertus Magnus and Roger Bacon 97 

But there is another alchemy, operative and practical, which 
teaches how to make the noble metals, and colours and many other 
things better or more abundantly by art than they are made in 
Nature. And the science of this kind is greater than all those pre- 
ceding because it produces greater utilities. For not only can it 
yield wealth and very many other things for the public good, but it 
also teaches how to discover such things as are capable of pro- 
longing human life for much longer periods than can be accom- 
plished by Nature. ... It confirms theoretical alchemy through its 
works and therefore confirms natural philosophy and medicine, 
and this is plain from the books of the physicians. For these authors 
teach how to sublime, distil and resolve their medicines, and by 
many other methods according to the operations of that science, 
as is clear in health-giving waters, oils and many other things. 

Bacon was thus one of the first to distinguish between the 
study of chemistry for its own sake and the study of chemistry 
on account of its valuable technical and practical applications. 
Except, however, for the fact tbat he minimized the importance 
of the Aristotelian 'prime matter' and made fuller use of the 
theory of the Four Elements, he differs very little from the other 
alchemists in his conception of alchemical theory and practice. 
He accepts the sulphur-mercury theory, which he appears to 
have taken over bodily from Avicenna, and is quite as credulous 
on the subject of transmutation as any of his contemporaries. 
He clearly had a wide knowledge of the Arabian authors, whom 
He read in the original Arabic, and he seems to have perceived 
that in chemistry must be sought the science which should fill 
the gap between Aristotelian physics and the biological sciences. 
As to actual discoveries in chemistry, there is no evidence that 
he made any; and the famous 'cipher' in which he was supposed 
to describe the preparation of gunpowder has recently been 
shown to be a copyist's blunder. 

Bacon's services to chemistry were roughly these : he gave an 
accurate picture of contemporary alchemical thought, explained 
its methods and aims with lucidity, saw that it had a great future 
as an experimental science, and appreciated (within the limits 
noted) the importance of an experimental basis for natural 

2613-4 H 

98 Popular Books and the Technical Tradition 

science. But it is rather as the epitome of his age than as a 
thinker in advance of his age that we ought to regard him. 

Of Raymond Lully and Arnold of Villanova there is little that 
need be said. Many chemical works are ascribed to Lully 
the celebrated missionary to the Moors but Mrs. Singer has 
recently shown that they are all spurious and probably of a much 
later date. Arnold of Villanova's voluminous works are chiefly 
concerned with medical subjects, and chemistry is dealt with 
only incidentally; still, Arnold was widely read and was familiar 
with the books of the chief Muslim chemists, and a study of his 
chemical ideas would doubtless be a very useful piece of re- 
search. On the whole, the twelfth and thirteenth centuries may 
be regarded as a time of assimilation, when the chemical know- 
ledge of Islam was being absorbed into Europe : it is only much 
later that a fresh efflorescence occurred. 

30. Popular Books and the Technical Tradition 

TURNING aside from the work of the great men of the period, let 
us now pass in review one of the many popular books written for 
the instruction of the laity and the less well educated among the 
clergy. Such books were generally in the form of an encyclo- 
paedia, giving a conspectus of the whole realm of contemporary 
knowledge. One of the most famous of them was Bartholomew 
the Englishman's book On the Properties of Things, written by an 
English Franciscan about 1260. The great popularity it attained 
shows that there was a keen public demand for learning ; and its 
success was by no means confined to England. The Emperor 
Charles V, in 1372, ordered it to be translated into French, 
while Spanish and Dutch translations quickly followed. Ori- 
ginally written in Latin, it appeared in English in 1397, and as 
many as seventeen editions of the various versions were pub- 
lished in the course of the fifteenth century. 

Two extracts from Mr. Robert Steele's edition of the English 
text will serve to show us the kind of chemistry current, in the 
thirteenth century, among educated men like Bartholomew. 
The first describes the 'discovery' of glass, reproducing a very 


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^ m 

:* ^ 

no s^ 

'oa <P* ft* I' 


It ftii 

Ifttfi* 0* tt?0 g ^ 

r qu Pirft t pit 

jMte ffit ft Ptttt to 

cris t f ^ *ft^t a! 

tt * 

Mb* tt 1 t 

to tftl qui i: 

li ttit ft 

te f ftti * r *. 


. Sfe 

fit m i^c p 

... : *. - . i _ ik . ;; ^. _ - -, ; - : ; -__ 


H 2 

ioo Popular Books and the Technical Tradition 

old story, and the second discusses the nature of quicksilver and 

the constitution of the metals. 

Glass, as Avicen saith, is among stones as a fool among men, for it 
taketh all manner of colour and painting. Glass was first found 
beside Ptolomeida in the cliff beside the river that is called Vellus, 
that springcth out of the foot of Mount Carmel, at which shipmen 
arrived. For upon the gravel of that river shipmen made fire of 
clods medlied with bright gravel, and thereof ran streams of new 
liquor, that was the beginning of glass. It is so pliant that it taketh 
anon divers and contrary shapes by blast of the glazier, and is 
sometimes beaten, and sometimes graven as silver. And no matter 
is more apt to make mirrors than is glass, or to receive painting; 
and if it be broken it may not be amended without melting again. 
But long time past, there was one that made glass pliant, which 
might be amended and wrought with an hammer, and brought 
a vial made of such glass before Tiberius the Emperor, and threw 
it down on the ground, and it was not broken but bent and folded. 
And he made it right and amended it with a hammer. Then the 
emperor commanded to smite off his head anon, lest that his craft 
were known. For then gold should be no better than fen, and all 
other metal should be of little worth, for certain if glass vessels 
were*not brittle, they should be accounted of more value than 
vessels of gold. 

Quicksilver is a watery substance medlied strongly with subtle 
earthly things, and may not be dissolved and that is for great dry- 
ness of earth that melteth not on a plain thing. Therefore it 
cleaveth not to thing that it toucheth, as doth the thing that is 
watery. The substance thereof is white : and that is for clearness of 
clear water, and for whiteness of subtle earth that is well digested. 
Also it hath whiteness of medlying of air with the aforesaid things. 
Also quicksilver hath the property that it curdeth not by itself 
kindly without brimstone: but with brimstone, and with sub- 
stance of lead it is congealed and fastened together. And therefore 
it is said, that quicksilver and brimstone is the element, that is to 
wit matter, of which all melting metal is made. Quicksilver is 
matter of all metal, and therefore in respect of them it is a simple 
element. Isidore saith it is fleeting, for it runneth and is specially 
found in silver forges as it were drops of silver molten. And it is 
oft found in old dirt of sinks, and in slime of pits. And also it is 

Popular Books and the Technical Tradition 101 

made of minium done in caverns of iron, and a patent or a shell 
done thereunder; and the vessel that is anointed therewith, shall 
be beclipped with burning coals, and then the quicksilver shall 
drop. Without this silver nor gold nor latten nor copper may be 
overgilt. And it is of so great virtue and strength, that though 
thou do a stone of an hundred pound weight upon quicksilver of 
the weight of two pounds, the quicksilver anon withstandeth the 
weight. And if thou doest thereon a scruple of gold, it ravisheth 
unto itself the lightness thereof. And so it appeareth it is not 
weight, but nature to which it obeyeth. It is best kept in glass vessels, 
for it pierceth, boreth, and fretteth other matters. 

We see that the critical faculty of our author is not very 
active, and that he is content to accept as true any information 
for which he can find authority. The section on quicksilver 
plainly betrays its Arabic origin, and goes back ultimately to 
Jabir by way of Avicenna. There is nothing new no original 
contribution by European scientists, no fresh theory by Euro- 
pean philosophers. The new science was still in process of be- 
coming naturalized, and the extent of the borrowing from Islam 
may be estimated not only by the numerous translations and 
quotations but by the scores of Arabic chemical terms taken over 
bodily into Latin alchemy. The following examples, chosen at 
random, are typical, and serve incidentally to demonstrate how 
impossible it is to understand medieval European alchemy 
without a previous knowledge of Muslim work : 

Abicum, Arabic, al-anbiq, alembic. 

Abric, A. al-kibrit, sulphur. 

Alcalai, A. al-qali, alkali. 

Alcazdir, A. al-qasdir, tin. 

Alchitram, A. al-qitran, pitch. 

Alchohol, A. al-kuhl, kohl (stibium, Sb 2 S 3 , or galena, PbS). 

Aliocab, A. al-'uqab, 'the eagle' (sal-ammoniac). 

Almizadir, A. al-nushadhir, sal-ammoniac. 

Anticar, A. al-tinkar, borax. 

Appebriock, A. al-kibrit, sulphur. 

Asabon, A. al-sabun, soap. 

IO2 Popular Books and the Technical Tradition 

Ased, A. asad, lion. 

Athanor, A. al-tannur, furnace. 

Azarnet, A. al-zarnikh, arsenic [sulphides]. 

Baul, A. haul, urine. 

Bayda, A. al-baida, egg [name of a piece of apparatus]. 

Daeb, A. dhahab, gold. 

Danic, A. daniq, a certain weight. 

Dem, A. damm, blood. 

Faulex, A. fulad, steel. 

Fom, A. fum, month. 

lladid, A. hadid, iron. 

Hager, A. hajar, stone. 

Kald y A. khall, vinegar. 

Kamar, A. qamar, silver moon. 

Khamir, A. kharnir, ferment. 

Luban, A. luban, gum, resin. 

Lubanjawa, gum of Java, was corrupted into Benjawin, or 

benzoin, whence our 'benzene'. 
Malek, A. milh, salt. 

Martach, A. martak, litharge or massicot. 
Merdasingi, A. mardasanj, litharge. 
Misadir, A. nushadhir, sal-ammoniac. 
Nar, A. nar, fire. 
Noas, A. nuhas, copper. 
Nora, A. nura, lime. 

Obelchera, A. abu'l-qar'a, large cucurbite. 
Ocob, A. uqab, eagle [sal-ammoniac]. 
Rusatagi, A. rusakhtaj, black oxide of copper. 
Tain, A. tin, clay. 
Usifur, A. zanjifar, cinnabar. 
Zaibar, A. zaibaq, mercury. 
Zaibuch, A. zaibaq, mercury. 
Ziniar, A. zinjar, verdigris. 

In considering the rise of chemistry in Europe, one should not 
forget the technical tradition, carried on by humble craftsmen 

Popular Books and the Technical Tradition 103 

and artisans, and more or less continuous throughout the ages. 
Most of these technical workers are nameless and the records of 
their work are, as would be expected, but scanty. At least three 
books of importance have, however, survived the vicissitudes of 
time and remain to bear witness to the vast amount of laborious 
practical investigation that was carried on in what some are 
pleased to call the Dark Ages. These three books are known as 
the Compositiones ad tingenda, the Mappae Clavicula and the 
Liber ignium ad comburendos hostes. 

The Compositiones ad tingenda is known in a manuscript that 
dates from the time of Charlemagne (r. 742-814). It is not a 
systematic treatise but a collection of recipes, probably gathered 
together by some technical worker for his own use in the arts. 
It deals with such varied subjects as the dyeing of skins, the pre- 
paration of coloured glass, methods of writing in letters of gold, 
the gilding of copper and other metals, and a description of the 
various metals, minerals, earths and herbs that found technical 
application. It is believed that many of the recipes are of 
Byzantine origin, while some are still more ancient, having been 
found in the famous Ley den papyrus. The work, as a whole, is 
noticeable for the complete absence of superstition in it. We 
here meet, too, for the first time with the names vitriol (given 
to an impure sulphate of iron obtained by the weathering of 
pyrites), and bronze, which has been derived probably by a 
false etymology from Brundisium (Brindisi), where the alloy 
has been stated to have been prepared on a large scale. 

The Mappae Clavicula (the earliest known manuscript is of 
the tenth century and is at Schlestadt) includes practically all 
the recipes of the Compositiones ad tingenda, and adds a great 
many more. It is noteworthy that a large number of the new 
recipes deal with transmutation, a subject which is scarcely 
mentioned in the earlier work. A later manuscript of this work, 
written in the twelfth century, contains the earliest account of 
the preparation of alcohol, expressed in the following sentence: 
De commixtione puri et fortissimi xkok cum HI qbsuf tbmkt cocta 
in ejus negocii vasts fit aqua quae accensa flammam incumbustam 

104 Popular Books and the Technical Tradition 

servat materiam. The riddle of the three words in cipher was 
solved by Berthelot, who showed that each letter stood for that 
which precedes it in the alphabet. Thus xkok is vini y qbsuf is 
parte, and tbmkt is salts \ the passage may then be translated as 
follows : 'On mixing a pure and very strong wine with a third of 
a part of salt, and heating it in vessels suitable for the purpose, 
an inflammable water is obtained which burns away without 
consuming the material [on which it is poured]. * 

The third book, the Liber ignium ad comburendos hostes, of 
'Marcus Graecus', appears to be a translation from the Arabic. 
No Arabic original is known, however, nor is anything known of 
its author. The earliest manuscript is of the early fourteenth 
century (perhaps, indeed, of the year 1300). Its recipes may be 
divided into four groups: those for (i) incendiary substances, 
(2) phosphorescent substances, (3) 'Greek fires', and (4) ex- 
plosives containing saltpetre. Among them is one for the pre- 
paration of gunpowder: 'Take i Ib. of live sulphur, 2 Ib. of 
charcoal from the lime or willow, 6 Ib. of saltpetre. Let the 
three substances be very finely powdered upon a marble slab 
[and then mixed together].' This is one of the earliest mentions 
of gunpowder, although Roger Bacon, in his Opus Tertium, 
says that at that time (1267) it was already in common use for 
children's fireworks. 

Two further examples may suffice to illustrate the practical 
chemical knowledge of the time. The first of them is taken from 
an English work (hopefully ascribed to Hermes) called The Book 
of Quintessence. It describes very lucidly how to convert gold 
into a powder or calx and also how to 'part' silver from gold : 

The science to brynge gold into calx. Take fyn gold and make it 
into small lymayl. take a crusible with a good quantity of Mercuric, 
and sette it to a litil fier so that it vapoure not, and putte therinne 
thi lymail of gold, and stire it weel togidere and aftirward withinne 
a litil tyme ye schal se al the gold withinne the Mercuric turned 
into erthe as sotil as flour, thanne yeue it a good fier that the 
Mercuric arise and go his wey, or ellis and ye wole ye may distille 
and gadere it, putty nge therupon a lembike and in the corusible ye 

Popular Books and the Technical Tradition 105 

schal fynde the gold calcyned and reducid into erthe. And if ye 
wole not make lymayl of gold, thanne make therof a sotil thinne 
plate, as ye kan, and putte withinne the Mercuric al warm, and ye 
schal haue youre desier. And in this same maner ye may worche 
with siluir. Thanne take the calx of these two bodies, and here 
hem openly with you. and ther schal noman knowe what thei ben. 
. . . Now I wole teche you the maistrie of departynge of gold fro 
siluir whanne thei be meyngid togidere. Forsothe ye woot weel 
that ther be manye werkis in the whiche gold and siluir be meyngid, 
as in giltynge of vessel and lewellis therfore whanne ye wole drawe 
the toon from that othir. putte ai that mixture into a strong watir 
maad of vitriol and of sal petre. and the silyur wole be dissolued, 
and not the gold, thanne ye haue that oon departid fro the tothir. 
And if ye wole dissolue ye gold to watir. putte thanne yn the watir 
corosyve. Sal armoniac. and that watir withoute doute wole 
dissolue gold into watir. 

The second extract is taken from a painter's recipe-book of 
the thirteenth century and serves very well to illustrate the 
empirical chemistry of the medieval craftsman : 

On making verdigris. If you wish to make verdigris, take a new pot, 
or any other hollow vessel, and put into the vessel some very strong 
vinegar, and arrange sheets of the purest copper over the vinegar, in 
such a way that they may not come into contact with the vinegar. 
And so cover it up, and seal it, and put it in a warm place, or 
underground, and set it aside for six months. And then you must 
open the vessel, and scrape off into a very clean dish the material 
which you find in it, and set it in the sun to dry. Furthermore, if 
you wish to make Rouen-green, take some sheets of very pure 
copper, and smear them all over with the best soap, and put these 
sheets into a clean vessel, made for the purpose, and fill it with 
pure vinegar. But arrange the sheets above it, in such a way that 
they may not come into contact with the vinegar. And when you 
have covered the vessel, seal it doubly ; and at the end of one month 
open it, and scrape what you find on the copper sheets into a dish, 
and dry it. 

The following are the instructions for making vermilion or 
cinnabar : 

On making vermilion. If you wish to make the finest vermilion, 

106 Paracelsus 

take a glass jar and lute it outside with the finest clay, three times ; 
and then take one weight of quicksilver and two weights of white 
or yellow sulphur, so that there will be two parts of sulphur and 
a third of quicksilver. And put in the above-mentioned in- 
gredients in such a way that part of the sulphur, finely divided, 
may be on the bottom, and part of the quicksilver above, so that it 
may reach right up to the neck of the jar. Put the jar upon four 
stones, and then build up a charcoal fire around the jar, but let it 
be a very moderate one. And so cover the mouth of the jar with 
a little tile or piece of stone. And when you see that the smoke is 
blue or yellow-coloured, as it comes off, put on the cover; and 
when you see that the smoke is almost as red as vermilion, take it 
from the fire, and you will have in the jar the finest vermilion. 

It is interesting to compare this last recipe with Jabir's in- 
structions for the preparation of the same substance, as given in 
a British Museum manuscript of his Great Book of Properties : 
To convert mercury into a red solid. Take a round glass vessel, 
and pour a convenient quantity of mercury into it. Then take 
a Syrian earthenware pot and into it put a little powdered yellow 
sulphur. Place the glass vessel on the sulphur and pack it round 
with more sulphur up to the brim. Place the apparatus in the 
furnace for a night, over a gentle fire . . . after having closed the 
mouth of the earthenware pot. Now take it out and you will find 
that the mercury has been converted into a hard red stone of the 
colour of blood. . . . This is the substance which men of science 
call cinnabar. 

31. Paracelsus 

THE impulse that deflected many chemists from their alchemi- 
cal pursuits and, in the sequel, did much to make chemistry 
once more a self-respecting science, came from that curious 
personality known as Paracelsus. Philippus Aureolus Theo- 
phrastus Bombastes von Hohenheim, or Paracelsus, was the 
son of a Swiss physician and was born at the village of Ein- 
siedeln, near Zurich, on 17 December 1493. As a boy, he 
was given elementary instruction in alchemy, astrology, medi- 
cine and surgery by his father, and at the age of sixteen entered 
the University of Basel. Some time later he proceeded to 


io8 Paracelsus 

Wiirzburg, to study under a celebrated expert in magic, alchemy 
and astrology, Hans von Trittenheim, generally known as 
Trithemius. It was doubtless during the time of his association 
with Trithemius an authority on the Kabbala and a follower of 
the Neo-Platonists that he became enamoured of occultism in 
general and of alchemy in particular. At the age of 22 he 
went to the mining school of Sigismund Fugger, in the Tyrol, 
where he worked for a year and was able to glean much valuable 
technical information concerning the precious metals and also 
to broaden his knowledge of alchemy proper, for Fugger was 
widely known as an expert alchemist. 

Of a restless disposition, Paracelsus seems to have been 
constitutionally incapable of remaining long in any one place. 
After learning all that Fugger could teach him, he set off on 
a rambling journey through Germany, Italy, France, the Nether- 
lands, Denmark, Sweden and Russia, and, according to some, 
may even have visited India. For a time he served as an army 
surgeon in the Danish wars, and managed to secure the degree 
of Doctor of Medicine though at what university remains 
undecided. During his travels he associated with physicians, 
alchemists, astrologers, apothecaries, miners, gipsies and adepts 
of occult science, returning to Germany in 1526 with a stock of 
curious knowledge such as few men can ever have possessed. At 
that time the celebrated book-publisher of Basel, Johannes 
Frobenius or Froben, was seriously ill, and hearing that Para- 
celsus was at Strasburg he sent to ask him to come and treat him. 
* Froben 's house in Basel was frequented by a number of 
scholarly persons, notably by Erasmus, who at that time lived 
in Froben 's house, and by Oecolampadius, then professor of 
theology in the University of Basel, both prominent in the 
reformation movement in Switzerland. Impressed by the per- 
sonality and medical skill of the new physician, these men and 
particularly, it is said, Oecolampadius prevailed on the city 
authorities (Stadtrath) to offer the then vacant position of city 
physician to Paracelsus, an offer which was at once accepted.' 
Frobenius appears to have been cured, for when Erasmus him- 

Paracelsus 109 

self was taken ill some time afterwards he wrote Paracelsus as 
follows : 'I cannot offer thee a reward equal to thy art and know- 
ledge I surely offer thee a grateful soul. Thou hast recalled 
from the shades Frobenius who is my other half: if thou 
restorest me also thou restorest each through the other. May 
fortune favour that thou remain in Basel/ l 

A man more unstated to hold public office than 'marvellous 
Paracelsus, always drunk and always lucid, like the heroes of 
Rabelais', can hardly be imagined. With a great conceit of his 
own powers and views and little regard for the opinions and 
feelings of others, he signalized his appointment as City 
Physician by publicly burning (in a brass pan, with sulphur and 
nitre) the works of Avicenna and Galen, to show his contempt of 
orthodox medicine and to emphasize the fact that his doctrines 
were essentially his own. 'If your physicians,' he said, 

only knew that their prince Galen they call none like him was 
sticking in hell, from whence he has sent letters to me, they would 
make the sign of the cross upon themselves with a fox's tail. In the 
same way your Avicenna sits in the vestibule of the infernal portal ; 
and I have disputed with him about his aunim potabile, his 
Tincture of the Philosophers, his Quintessence, and Philosopher's 
stone, his Mcthridatic, his Theriac, and all the rest. O, you 
hypocrites, who despise the truths taught you by a great physician, 
who is himself instructed by Nature, and is a son of God himself! 
Come, then, and listen, impostors who prevail only by the authority 
of your high positions! After my death, my disciples will burst 
forth and drag you to the light, and shall expose your dirty drugs, 
wherewith up to this time you have compassed the death of princes, 
and the most invincible magnates of the Christian world. Woe for 
your necks in the day of judgement! I know that the monarchy 
will be mine. Mine, too, will be the honour and glory. Not that I 
praise myself: Nature praises me. Of her I am born; her I follow. 
She knows me, and I know her. The light which is in her I have 
beheld in her; outside, too, I have proved the same in the figure of 
the microcosm, and found it in that universe. 

As may easily be imagined, such conduct did not increase the 
1 Stillman, Paracelsus, London, 1920. 

no Paracelsus 

popularity of this bizarre medical officer of health. But his 
vituperation did not confine itself to general attacks on the 
whole body of physicians : individual members as well felt the 
venom of his tongue. To one who had ventured to disagree with 
him he replied in the following terms : 

So then, you wormy and lousy Sophist, since you deem the 
monarch of arcana a mere ignorant, fatuous, and prodigal quack, 
now, in this mid age, I determine in my present treatise to disclose 
the honourable course of procedure in these matters, the virtues 
and preparation of the celebrated Tincture of the Philosophers for 
the use and honour of all who love the truth, and in order that all 
who despise the true arts may be reduced to poverty. By this 
arcanum the last age shall be illuminated clearly and compensated 
for all its losses by the gift of grace and the reward of the spirit of 
truth, so that since the beginning of the world no similar germina- 
tion of the intelligence and of wisdom shall ever have been heard of. 
In the meantime, vice will not be able to suppress the good, nor 
will the resources of those vicious persons, many though they be, 
cause any loss to the upright. 

Before long Paracelsus became an object of hatred to all the 
druggists and apothecaries in the town, as well as to his brother 
physicians. At length matters were brought to a crisis. A pro- 
minent citizen of Basel had offered 100 guldens to any physician 
who would cure him. Paracelsus accepted the offer and cured 
his patient, who thereupon refused to pay the fee that had been 
agreed upon. Paracelsus sued him, but as might have been 
expected lost his case, a result which so infuriated the hot- 
tempered physician that he abused the judges in the roundest 
terms, and with a typically Paracelsan collection of libellous 
epithets. Warned that he had thus laid himself open to severe 
punishment, he left Basel secretly and hurriedly, setting out 
once more upon a life of wandering. In succeeding years we 
find him in many towns of Germany and Switzerland, but at 
last he was invited to Salzburg by the Prince Palatine, Duke 
Ernst of Bavaria, himself a keen student of the occult arts. 
Here he seems to have found a restful and congenial atmosphere, 

Paracelsus 1 1 1 

but he was destined to enjoy it for only a short time. On 
24 September 1541 he died, at the early age of 48 years a 
comparatively young man yet physically worn out by the restless 
and strenuous life he had led. His epitaph read: 

Here lies buried Philippus Theophrastus, distinguished Doctor of 
Medicine, who with wonderful art cured dire wounds, leprosy, 
gout, dropsy and other contagious diseases of the body, and who 
gave to the poor the goods which he obtained and accumulated. 
In the year of our Lord 1541 , the 24th of September, he exchanged 
life for death. 

We are told by a contemporary that Paracelsus was most 
laborious, and that he would often throw himself, fully dressed, 
booted and spurred, upon his bed and write ceaselessly for 
hours. He has, in fact, left us a large number of books upon 
medicine and chemistry, most of which are extremely difficult 
to understand on account of the unsystematic way in which 
their matter is arranged, and also on account of the * execrable 
style' which Paracelsus adopted. As Thomson bitterly exclaims, 
'how can we look for a regular system of opinions from a man 
who generally dictated his works when in a state of intoxication, 
and thus laboured under an almost constant deprivation of 
reason?' It is consequently a somewhat exasperating task to 
attempt to ascertain exactly what definite advances in knowledge 
Paracelsus actually made. That he was an accomplished ex- 
perimenter is certain, and among other items of chemical infor- 
mation scattered throughout his books are references to zinc, 
* cobalt* and bismuth (though he himself did not discover any of 
these metals), to the fact that a gas is given off when iron is dis- 
solved in dilute sulphuric acid, to the bleaching action of sulphur 
dioxide, and to several further observations that bear witness 
to his laboratory experience. He showed, too, that the alums 
differ from the vitriols, since the latter are derived from a metal 
but the former from an 'earth', i.e. a metallic oxide which at 
that time could not be reduced to metal. It was Paracelsus who 
first gave the name alcohol to spirit of wine. Originally signify- 
ing the black eye-paint used by Eastern women, al-kuhlor al-kohol 

ii2 Paracelsus 

had gradually acquired the meaning of any very finely divided 
powder ; thence by a natural transference it came to mean 'the 
best or finest part' of a substance. Possibly Paracelsus regarded 
spirit of wine as the 'best part' of wine, and therefore named it 
alcohol of wine or simply alcohol. This usage of the word has of 
course persisted, and the older meaning is now entirely obsolete. 
If, then, Paracelsus 's actual discoveries were but meagre, why 
is he to be included among the great 'makers of chemistry'? 
The answer to this query lies in his emphatic opinion as to the 
aim of chemistry. Alchemy, defined as the art of transmuting 
the metals, he certainly believed to be possible; yet he regarded 
the efforts of the alchemists as a waste of energy which might be 
better employed. Like the great Razi, he considered that one 
of the chief objects of chemistry should be the preparation and 
purification of chemical substances for use as drugs, and urged 
chemists, apothecaries and physicians alike to devote themselves 
to experiments with this object. We must remember that the 
apothecaries of that time usually had no knowledge of chemistry, 
preparing their medicines from roots, leaves, fruits, syrups and 
the like in the fashion of a village housewife. The physicians 
were in no better case. 'They think it suffices', says Paracelsus, 
'if, like apothecaries, they jumble a lot of things together and say 
"Fiat unguentum". . . . Yet if medicine were handled by artists 
[i.e. chemists], a far more healthy system would be set on foot.' 
For the few apothecaries and physicians who were enlightened 
enough to study chemistry and brave enough to apply chemical 
remedies, he had the warmest praise: 

I praise the spagyric chemical physicians, for they do not consort 
with loafers or go about gorgeous in satins, silks and velvets, gold 
rings on their fingers, silver daggers hanging at their sides, and 
white gloves on their hands, but they tend their work at the fire 
patiently day and night. They do not go promenading, but seek 
their recreation in the laboratory, wear plain leathern dress and 
aprons of hide upon which to wipe their hands, thrust their fingers 
amongst the coals, into dirt and rubbish and not into golden rings. 
They are sooty and dirty like the smiths and charcoal-burners, and 

Paracelsus 113 

hence make little show, make not many words and gossip with 
their patients, do not highly praise their own remedies, for they 
well know that the work must praise the master, not the master his 
work. They well know that words and chatter do not help the sick 
nor cure them. . . . Therefore they let such things alone and busy 
themselves with working with their fires and learning the steps of 
alchemy. These are distillation, solution, putrefaction, extraction, 
calcination, reverberation, sublimation, fixation, separation, re- 
duction, coagulation, tinction, &c. 

The relentless war that Paracelsus waged against contem- 
porary medicine had the effect of making chemistry, for the 
future, an indispensable part of a medical training. Physicians 
were set free from slavish deference to authority, and chemistry, 
presented with a new aim, was released from the trammels of 
degenerate alchemy. After this time, 'the art of chemistry was 
cultivated by medical men in general it became a necessary part 
of their education, and began to be taught in colleges and medical 
schools. The object of chemistry came to be, not to discover the 
philosopher's stone, but to prepare medicines; and a great 
number of new medicines, from both the mineral and vegetable 
kingdoms some of more, some of less, consequence, soon issued 
from the laboratories of the chemical physicians/ The im- 
portance of the new valuation of chemistry can scarcely be 
exaggerated. As long as alchemy and chemistry were synony- 
mous terms, the exponents of the Art (or science) were living 
under a growing cloud of suspicion and contempt. Quickly 
hardening into a rigid mould, alchemy was practised on stereo- 
typed lines and on its theoretical side was fast becoming a chaos 
of superstitious verbiage. Paracelsus's vigorous onslaught on 
orthodox medicine and his call to the chemists to prepare drugs 
provided a much-needed stimulus. The honourable task of the 
age of iatrochemistry, or medical chemistry, that he inaugurated, 
was to make the way clear for a reasonable medicine ; but it did 
more it made the way clear also for a reasonable chemistry. 

Before leaving Paracelsus for his successors, we may take a 
brief glance at his chemical theory, in so far as it may be 

2613-4 j 

ii4 Paracelsus 

disentangled from the cabbalistic ideas everywhere intertwined 
with it. Like the Neo-Platonists (of whose teachings there was 
a revival at this time), Paracelsus believed that the universe as 
a whole and all the objects in it were endowed with life. Inter- 
mediate between the material and immaterial were beings con- 
sisting of a body and spirit but no soul ; such were the sylphs of 
the air, the nymphs of water and the salamanders of fire which 
will be familiar to many from the alchemist in La Rotisserie de la 
Reine Pedauque. As to material substances, these are ultimately 
composed of the four Aristotelian elements, but immediately of 
three primary bodies, tria prima, viz. salt (body), sulphur (spirit) 
and mercury (soul). Paracelsus was thus taking over a previously 
existing modification of the old sulphur-mercury theory of 
metals, extended so as to apply to all substances whether metallic 
or not. Salt was the principle of incombustibility and non- 
volatility; mercury was the principle of fusibility and volatility; 
while sulphur was the principle in virtue of which substances are 
inflammable. This theory is, of course, not to be taken literally : 
the 'sulphur' in wood, for instance, is not the same as the 
'sulphur' in lead, and neither of them is to be conceived as very 
closely resembling ordinary sulphur. These tria prima are, 
indeed, nothing more than abstractions of qualities, and there- 
fore differ essentially in character from the elements of modern 
chemistry. Paracelsus himself says : 

You should know all seven metals originate from three materials, 
namely, from mercury, sulphur, and salt, though with different 
colours. Therefore Hermes has said not incorrectly that all seven 
metals are born and composed from three substances, similarly 
also the tinctures and philosopher's stone. He calls these three 
substances spirit, soul and body. But he has not indicated how 
this is to be understood nor what he means by it. Although he may 
perhaps have known, yet he has not thought (to say) it. I therefore 
do not say that he has erred, but only kept silent. But that it be 
rightly understood what the three different substances are that he 
calls spirit, soul and body, you should know that they mean not 
other than the three principia, that is mercury, sulphur and salt, 

Later latrochemists 115 

out of which all seven metals originate. Mercury is the spirit, 
sulphur is the soul, salt the body. 

[But] as many as there are kinds of fruits so many kinds there 
are of sulphur, salt, and so many of mercury. A different sulphur is 
in gold, another in silver, another in lead, another in iron, tin, &c. 
Also a different one in sapphire, another in the emerald, another 
in the ruby, chrysolite, amethyst, magnets, &c. Also another in 
stones, flint, salts, springwaters, &c. And not only so many kinds of 
sulphur but also as many kinds of salt, different ones in metals, 
different ones in gems, stones, others in salts, in vitriol, in alum. 
Similarly with mercuries, a different one in the metals, another in 
gems, and as often as there is a species there is a different mercury. 
Of one nature is sulphur, of one nature salt, of one nature mercury. 
And further they are still more divided, as there is not merely one 
kind of gold but many kinds of gold, just as there is not merely one 
kind of pear or apple but many kinds. Therefore there are just as 
many different kinds of sulphurs of gold, salts of gold, mercuries of 

The views on chemical philosophy peculiar to Paracelsus need 
j not unduly delay us, however, for they soon became obsolete and 
of themselves bore but little fruit. We may, in fact, legitimately 
suspect that even their author was not always certain of what he 
\ meant by his emphatically dogmatic statements on chemical 
theory. Their most valuable feature was their revolutionary 
character, and the worlds of medicine and alchemy, rudely 
awakened by Paracelsus 's vitriolic tongue, never afterwards 
relapsed into their former state of undignified but self-satisfied 
somnolence. Study Nature, said Paracelsus, for 'in her mysteries 
you will have enough to last you all your life . . . without re- 
ferring to paper books ' . ' This has been my Academy, not Athens , 
or Paris, or Toulouse.' 

32. Later latrochemists 

AFTER the death of Paracelsus, a bitter strife broke out between 
his followers and the supporters of the old methods of pharmacy 
and medicine. Many of the Paracelsan school were even more 
unrestrained than their master, and administered extraordinary 
not to say dangerously poisonous drugs to their unfortunate 

I 2 

n6 Later latrochemists 

patients. Whatever may be said in depreciation of the 'Galenical 
liquors' their 'Maukish, Spiritless, Dull, Flat Posset-drink, 
Small-beer, Early- water, loathsome Decoctions of cooling crude 
Herbs, Pippin Liquors, and the like, which starve the Vital 


Spirit, bringing a numness upon it', it is hard to believe that the 
following iatrochemical suggestions were any more efficacious : 
Cinnabar, to scatter 'those black Clouds arising from the horrid 
Spectrums of the Appoplexie, Epilepsie, introducing instead 
thereof a brightness and splendour in the Spirit' ; zinc sulphate 
for the eyes, to cause 'the Species of Objects to be seen more 

Later latrochemists 117 

plain' ; mercury, to destroy 'all sorts of Worms' ; lead acetate, to 
'Clarifie the Spleen, Reforming it's peccant Idea's'; and iron 
sulphide to cure diabetes. 

Such excesses were vigorously opposed by several chemists, 



notably Andreas Libavius (1540-1616). Born at Halle, Libavius 
practised for some years as a doctor, but in 1588 went to Jena 
as professor of history in the university there. Later he taught at 
the Gymnasium at Rothenburg on the Tauber, and from 1607 
till his death he was director of the Gymnasium at Coburg. 
Though not an extreme reactionary, Libavius had little sympathy 

n8 Later latrochemists 

with Paracelsan views, and carried on controversies with many 
of the wilder iatrochemists. He was ready to admit the value of 
chemical remedies, but sought to establish clearly a distinction 
between experimental truth and imaginative hypothesis. In 
chemical theory he has no claim to originality ; at times he seems 
to support the Paracelsan theory of the triaprima y salt, sulphur 
and mercury, and at others he reverts to the older Arabian 
sulphur-mercury theory. It is rather on the practical side that 
Libavius attracts our attention. In 1595 he published his great 
work Alchymia, which was for many years the chief chemical 
text-book. It is a comprehensive survey of contemporary 
chemical knowledge and has earned its author an undying fame. 
The keynote throughout is one of system and plain exposition, 
and though it is mainly a compilation it contains much that is 
new. Libavius was, for instance, the first to show that sulphuric 
acid can be made by burning sulphur with saltpetre, and proved 
that the acid so obtained was identical with that prepared by 
distilling green vitriol or alum; he discovered stannic chloride, 
which he prepared by heating tin with mercuric chloride; he 
first described ' glass of antimony' and the blue colour given by 
ammonia with copper salts; and he developed a rudimentary 
system of chemical analysis. 

Libavius also devoted much thought to the design and equip- 
ment of chemical laboratories. Figures 29 and 30 show respec- 
tively the elevation and ground-floor plan of his ideal 'chemical 
house', containing, besides the main laboratory, a store-room 
for chemicals, a preparation room, a room for the laboratory 
assistants, a room for crystallization and freezing, a room for 
sand and water baths, a fuel room and, not least among the 
amenities, a wine cellar a delightful feature unhappily over- 
looked by the modern architect of chemical laboratories ! In the 
main room, apparatus was arranged round the walls ; it included 
a great variety of furnaces, descensories, sublimatories, dis- 
tillation apparatus, crucibles, mortars and phials. Very sig- 
nificant is the absence of a balance-room : chemistry was not yet 
a quantitative science. As a whole, Libavius 's chemical house, 

van Helmont 119 

in its workmanlike design and orderly plan, contrasts very 
strongly with the usual alchemical laboratory of the time, of 
which we can get a good impression from the pictures drawn by 
Peter Breughel (c. 1525-69), John Stradanus (c. 1530-1605), 
J. Pinas (c. 1600), David Teniers the younger (1610-90) and 
John Steen (1626-79). Libavius may, in fact, be said to have 
planned the first chemical, as opposed to alchemical, laboratory. 

33. van Helmont 

ONE of the last and certainly the greatest of the iatrochemists 
proper was Johann Baptista van Helmont, born at Brussels in 
1577 of a noble and wealthy Brabant family. By the age of 
seventeen he had completed an Arts course at the University of 
Lou vain, but he declined to take a degree on the grounds that he 
was dissatisfied with what he had been taught. Turning to 
science, mathematics and philosophy, he found them equally 
unsatisfactory, and after dallying with mysticism for some time 
he took up the study of medicine. Here he found his true bent, 
and when he graduated at Louvain in 1599 he astonished his 
examiners by the extent of his learning. Falling ill a short time 
later, he was attended by a Galenist physician, whose treatment 
unfortunately proved a failure, van Helmont consequently 
determined to exert himself to overthrow what was left of the 
orthodox system of medicine, and joined the ranks of the Para- 
celsan school; he was, however, too original and independent 
a thinker to follow Paracelsus blindly and had no hesitation in 
differing from 'the immortal Theophrastus' when he thought fit. 
After an extended tour throughout Europe he returned to the 
Netherlands deeply impressed with the importance of chemistry. 
Having married a rich Brabant lady, Marguerite van Ranst, he 
settled at Vilvorde, near Brussels, and for the rest of his life shut 
himself up in his laboratory pursuing chemical investigations 
and writing scientific books. His fame became so great that he 
received many flattering offers from German princes to accept 
an official position at their Courts, but he could not be induced 
to leave his beloved laboratory. He died at Vilvorde on 30 

I2O van Helmont 

December 1644. His writings were gathered together after his 
death by his son, under the title Ortus medicinae, and published 
by the famous house of Elzevir at Leyden. An English transla- 
tion, by John Chandler, appeared in 1662. 

van Helmont resembled Paracelsus in his intense inclination 
to the supernatural, his trenchant style and his bitter contempt 
of the Galenists ; but in disposition and character the two were 
very different. Modest and unassuming, van Helmont found 
his pleasure in the patient investigation of scientific subjects 
rather than in the meretricious splendour of a princely court. 
For chemistry, the choice was a happy one. 

In chemical theory, van Helmont was more reactionary than 
Libavius, and, neglecting both the Aristotelian elements and the 
iatrochemical tria prima, he harks back to an ancient Greek 
theory (due to Thales) that water is the true principle of all 
things. Mercury, salt and sulphur, he says, which the chemists 
call the three primary bodies, are not in reality principles, i.e. 
elements, since (a) there are bodies in which they do not exist, 
(b) they are themselves formed from water, and (c) they can be 
reconverted into water. His belief that water is the essential 
principle of all things was not a mere imaginative flight; he 
adduced both observation and experiment in support of it. 
Thus he draws attention to the fact that an enormous number of 
both organic and inorganic substances yield water when strongly 
heated, and described the following experiment, which may well 
have appeared quite conclusive : 

He took 200 pounds of earth dried in an oven, and having put it 
into an earthen vessel and moistened it with rain water, he planted 
in it the trunk of a willow tree of five pounds weight; this he 
watered, as need required, with rain or distilled water ; and to keep 
the neighbouring earth from getting into the vessel, he employed 
a plate of iron tinned over and perforated with many holes. Five 
years having elapsed, he took out the tree and weighed it, and (in- 
cluding the weight of the leaves that fell during the four autumns) 
he found it to weigh 169 pounds 3 ounces. And having again dried 
the earth it grew in, he found it only about 2 ounces short of its 

van Helmont 121 

former weight of 200 pounds; so that 164 pounds of the roots, 
leaves, wood, and bark, which constituted the tree appeared to 
have sprung from the water alone. 

We know now that the source of the increase in weight was not 
merely the water, but also the carbon dioxide of the air, but we 
can readily admit that, in the absence of any knowledge of the 
constitution of the atmo- 
sphere and the relation be- 
tween atmospheric gases and 
plant life, van Helmont's 
experiment must have ap- 
peared to him to provide irre- 
futable evidence of the truth 
of his theory. In this con- 
nexion, it is interesting to 
find that van Helmont was 
the founder of pneumatic 
chemistry; it is, indeed, by 
his work on gases that he will Fi s- 

be chiefly remembered. He 
was not successful in collecting them, although he made many 
attempts to do so, but he it was who first realized that here was 
a new and important class of substances, and who, in fact, 
actually invented the word gas (from * chaos') by which to 
designate them. It is unnecessary to point out the incalculable 
results of van Helmont's observations one has only to re- 
member that the development of the atomic and molecular 
theories by Dalton, Gay-Lussac and Avogadro was based very 
largely upon work on gases to realize that van Helmont opened 
the way to one of the most fruitful fields of chemistry. He had 
not the good fortune to hit upon the beautifully simple idea of 
the pneumatic trough so obvious to us, but in its discovery 
a mark of genius and broke innumerable vessels in vain 
attempts to isolate the 'wild invisible spirits, which will not be 
pent up'. As Hoefer remarks: 'Que de vaisseaux brises avant 
que Ton parvint a recueiller les fluides elastiquesF It is pleasant 


122 van Helmont 

to think that the solution of this tremendous problem is mainly 
the honour of the Englishmen, Hales and Priestley, though 
Boyle too had used a method of collecting gases over water. 

van Helmont's gas silvestre was carbon dioxide. He showed 
that it was formed when charcoal was burnt, and when beer and 
wine were fermented, and he also detected it in the air of the 
Grotto del Cane (Naples). He discovered its presence in the 
mineral waters of Spa, and prepared it by the action of acetic 
acid upon a carbonate. He believed, too, that the same gas was 
evolved when silver was dissolved in nitric acid, since his only 
test was to find whether the gas would extinguish a flame or 
whether it would itself burn. An inflammable gas obtained from 
the intestines and by the fermentation of dung he called gas 
pingue. In short, van Helmont showed that gases were distinct 
substances, with definite properties, but, owing to his inability 
to collect them, he was able to distinguish only two kinds, 
namely, inflammable (gas pingue) and those which would not 
support combustion (gas silvestre). 

A last point of interest in connexion with van Helmont is that 
he clearly recognized the law of the conservation of matter, at 
least in particular cases, and realized that substances continue 
to exist even after undergoing chemical change. Thus he 
showed that if a certain weight of silica is converted into water- 
glass and the latter then treated with acid, the precipitated silicic 
acid will on ignition yield the same weight of silica as that 
originally taken. Yet in spite of his keen scientific insight and 
his powers as an experimentalist, he retained a firm belief in the 
possibility of the transmutation of the metals, and one of the 
most circumstantial of all accounts of supposed transmutation is 
vouched for by him. 

In 1618, van Helmont received at his laboratory at Vilvorde, from 
an unknown source, about a quarter of a grain of the philosophers' 
stone. He projected it upon 8 ounces of mercury, which was 
transformed into fine gold. From that day he became a warm 
partisan of alchemy, and even christened his new-born son with 
the name Mercurius. 'Mercurius van Helmont did not belie his 

124 Nicolas Lemery 

alchemical baptism, for he converted Leibniz to this way of 
thinking ; during the whole of his life the latter sought the philo- 
sophers' stone, dying without having found it, it is true, but as 
a fervent disciple/ 

34. Nicolas Lemery 

BEFORE leaving the iatrochemists for Boyle and the beginnings 
of modern chemistry, we may take a passing glance at a succes- 


sion of accomplished French chemists who flourished in the 
seventeenth and early eighteenth centuries at Paris. The work 
of all of them was on similar lines, largely coloured by iatro- 
chemical practice, and in itself it had little immediate effect upon 
chemical philosophy. We can, therefore, in a book of this size, 
conveniently consider it as a whole and so avoid the necessity of 
interrupting the main thread of our story in later pages. 

In 1606 chemistry received official recognition in France by 
the establishment of a Demonstratorship, and some years after- 






d'introdudion y tant pour rintclligcncc dcs Au- 
teurs qui ont traitedelaTheoncdecettc Science 
en general : Quepour faciliter Ics moycns dc faire 
amftement & methodicjueinem Ics operations 
fur les vcgetaux & fur lesmineraux , fans la pcrcc 
d'aucune des vertus dfenticllcs qu'ils contienncnt. 
'Par N. LE FE'VRE , *?rofeffettrT{oyal tn Chyme , ^por/- 
catre ordinaire A^T(oj d'*4nglcterrt &de fa Mtttfo> O* 
Mcmlre <le Vdicademic'Royale deLowlres. 

de Edition, revcuc, corrigcc &dc bcaucoiip 
augmentcc de bon nombre d'excellcns 
remedes , par 1'Authcur. 


thez THOMAS IOLLY , au Palais, en la Salle dcs 

Merciers,au coin de la Gallcrie dcs Prifonniers, 

a la Palme , & aux Armes d'Hollande. 

MT D C. TX I X. 


Fig- 34 



ia8 Nicolas Lemery 

wards it became part of the duty of the First Physician to the 
King to give public lectures on chemistry at the laboratories in 
the Jar din du Roi or Jar din des Plantes : a garden founded in 
1627 by Guy de la Brosse, Mathematician to the King, as a site 
for the cultivation of medicinal plants. The first demonstrator 
was the eminent Scottish doctor, William Davidson or 
d'Avisonne, as he preferred to call himself. He was succeeded 
by Jean Beguin, the author of a popular treatise entitled Les 
Clemens de Chymie, and by Nicolas Lefebure, who frankly stated 
that he drew from Paracelsus, van Helmont and others, and laid 
no claim to originality. According to Lefebure, there are three 
kinds of chemistry: (a) philosophical, i.e. scientific or contem- 
plative, which reflects upon nature and natural effects; (b) iatro- 
chemical, which is essentially practical but is inspired by the 
philosophical; and (c) pharmaceutical, which is merely operative, 
since the apothecaries must work only according to the direc- 
tions of the iatrochemists 'of whom', says Lefebure with 
a flourish, 'we have a veritable model in the person of M. Vallot, 
chosen by His Very Christian Majesty for his First Physician*. 
Shortly after the foundation of the Royal Society, Charles II 
summoned Lefebure to London, where he spent the rest of his 
life at the Court of St. James's. His post in Paris was filled by 
Christopher Glaser, who was afterwards forced to leave the 
country through becoming involved in the notorious poisoning 
case known as the affaire Brinvilliers : he was suspected of having 
supplied the amiable Marquise with the arsenic she employed 
to murder her father and brother. 

One of Glaser 's pupils was Nicolas Lemery, who, like many of 
the seventeenth-century chemists of France, belongs rather to 
the history of pharmacy than to that of chemistry. Yet his text- 
book entitled Cours de Chymie (first published in 1675) enjoyed 
an unparalleled success, going through eleven editions in France 
alone and being translated into English, Latin, German, Italian 
and Spanish. It consequently exerted a deep influence upon 
contemporary chemical thought and incidentally brought its 
author a handsome fortune by way of royalties. The chief 


O F 



The Eafleft Manner of perv 
formirig thofe Operations that are in 
life in PHTSICK. 


With many Curious Remarks and 

Ufeful Difcourfes upon each 


Writ in FRENCH by Monfieur 

TranHated by W A L T E R II A R R 1 S, 
Doftor of PHTSICK. 

L O 2^ 1> O 

Printed for Walter Kettilfy at the 

Head in.St. Caul's Church- Yard , 1677. 

Fig. 37 


130 Nicolas Lemery 

characteristics of Lemery were his rational outlook and his firm 
resolve to abolish completely the enigmatical and mystificatory 
language in which chemists still too often chose to enwrap their 
knowledge. In his preface he states explicitly that he will endeavour 
to render himself intelligible and to avoid the obscure expressions 
of previous authors : now this had been a common gambit since 
the days of Zosimos, but Lemery actually did what he promised, 
and his book can be read and understood with ease and certainty. 

Lemery admits the convenience of assuming that there are five 
chemical 'principles' of natural things, viz. Water, Spirit, Oil, 
Salt and Earth, but cautiously remarks that the word principle in 
chemistry must not be undersood in too rigid a sense: for the 
substances so called are only ' principles' in so far as our weak 
imperfect chemical analysis fails to divide them further. Now 
chemistry is an Art that demonstrates what it does (he says), so it 
recognizes as fundamental only such things as are palpable and 
demonstrable. 'The fond conceits of other Philosophers, con- 
cerning natural principles, do only puff up the Mind with Grand 
Idea's, but they prove or demonstrate nothing.' Instead of con- 
tenting ourselves with metaphysical conceptions, like that of a 
Universal Matter, 'it will be fit to establish some sensible ones'. 

The Cours de Chymte, a book of some 500 closely printed 
pages, describes in completely unequivocal language the prac- 
tical chemical knowledge of the time, including much that is due 
to Lemery himself. The descriptions are accompanied by 
shrewd observations, and the general impression left on the 
mind of a modern reader is that Lemery must have been one of 
the most acute and skilful experimenters France has ever pro- 
duced. Not the least interesting passage is that which describes 
the explosion of a mixture of air and hydrogen. It is true that 
Lemery did not properly appreciate the reaction, or the nature 
of the inflammable substance, and that the real 'discovery' of 
hydrogen was made only a century later, by Cavendish ; but the 
passage is worth quoting : 

If 3 Ounces of the Oil of Vitriol be put into a middle-sized Phial, 

with a long Neck, and to it 12 Ounces of Water; when the Mixture 

Nicolas Lemery 131 

grows warm, if an Ounce, or an Ounce and half of Iron File-Dust 
be thrown into it at several Times, there will arise an Ebullition, 
and a Solution of the Iron, which will produce white Vapours, that 
will rise and fill the Neck of the Phial. If one puts to the Aperture 
a lighted wax Candle, the Vapour will immediately take Fire, and 
at the same Time occasion a violent and a cracking Noise, and then 
go out. ... It also often happens that the Vapour will keep lighted 
like a Torch, at the Top of the Neck of the Phial, above a quarter of 
an Hour. . . . The Sulphur of the File-Dust being disengaged and 
rarified by the Oil of Vitriol, exalts itself in a Vapour very sus- 
ceptible of Fire. . . . Aquafortis, or the Spirit of Saltpeter, does not 
excite a Detonation. 

Lemery also describes the preparation of fulminating gold by 
the addition of aqueous ammonia to a solution of gold in aqua 
regia. lie explains the formation and properties of the substance 
as follows. When the gold is dissolved in the aqua regia it be- 
comes divided into extremely fine particles, which are kept in 
suspension [solution] by the sharp points of the acid particles, 
just as a piece of metal may be made to float if it is attached to 
wood. On the addition of ammonia, the acid points are weakened 
and the gold particles are thus precipitated; they are, however, 
impregnated with some part of the dissolvent, viz. 'the sharpest 
part* of the acid edges. On heating the fulminating powder, the 
'spirits' locked up in it 'violently divide the most compact Body 
of Gold to get out quickly'. 

However inadequate we may think the theories expressed in 
these two extracts, we must admit that they are reasonable and 
scientific in spirit, free from the taint of the occult. They are 
definitely an attempt to explain observed facts on rational 
grounds and as such must win our approval. The scientific 
attitude was, indeed, once again beginning to make its appearance 
in chemistry, and if we now leave Paris for Oxford we shall find 
its most celebrated protagonist in the person of Robert Boyle. 
During the journey, which is essentially a passage from the old 
to the new chemistry, we may spend our time in a brief review 
of the country we have already traversed. 

K 2 

132 Robert Boyle 

35. Review of Chemistry to the Time of Lemery 

IN this first part of the book we have seen how chemistry arose 
in an empirical way from the observations of ancient craftsmen. 
Particularly in Egypt metallurgical knowledge was of vital im- 
portance to the Crown, and metallurgy was therefore largely 
practised as a secret art under the control of priests and other 
Crown officials. In Greece and Alexandria philosophical 
schemes of the universe were elaborated, tending in later 
classical times to an involved mysticism. During the first three 
or four centuries of our era Gnostic and Neo-Platonist thinkers 
applied their doctrines to the supposed art of transmuting base 
metals into gold, and so a practical craft became a false science. 
It is in Islam that we at length meet with real chemists, in the 
modern sense of the word. Men like Jabir and Razi systema- 
tized chemical knowledge, evolved definite chemical theories, 
and established chemistry as a true science. Later chemists of 
Islam on the whole failed to maintain the standard set them, and 
magic and superstition again vitiated the young science. 

From Islam chemistry was transmitted bodily to Europe in 
the twelfth to fourteenth centuries, but unfortunately the 
alchemical aspect received most attention, and alchemy, rather 
than chemistry, was cultivated for two or three hundred years. 
Then, about 1500, Paracelsus reorientated chemistry and en- 
gaged it in the service of medicine. Though alchemy continued 
to flourish, the more reasonable chemists turned to the prepara- 
tion of drugs and thus the extent of practical chemical knowledge 
was increased by leaps and bounds. With extended knowledge 
came a more scientific spirit, exemplified by men like Libavius, 
van Helmont and Lemery. Men felt that weighty events por- 
tended and that chemistry was on the eve of great advances. 
How well that feeling was justified the remaining sections of 
this book will show. 

36. Robert Boyle 

UNTIL the declining years of the seventeenth century, the 
ultimate background of chemical theory was the Aristotelian 

Robert Boyle 133 

system of the Four Elements. For almost exactly two thousand 
years this system reigned supreme and unchallenged; it was 
modified, additions were made to it, it occasionally receded into 
a temporary obscurity, but it was always there and always 
formed the philosophical basis of theoretical chemistry and the 
justification of practice. But with the vastly increased number of 
experimental facts brought to light by the alchemists and, 
particularly, iatrochemists, the Aristotelian or 'peripatetic' 
theory was perceived to be growing less and less adequate as 
a scientific explanation of phenomena ; and many chemists gave 
it lip-service rather than a genuine belief. It was at length felt, 
in general unconsciously perhaps, that Fire, Air, Earth and 
Water could be regarded as the elements of material bodies in 
only a metaphysical sense: hence the three 'hypostatical prin- 
ciples' or triaprima of the iatrochemists, and the salt, spirit, oil, 
water and earth favoured by Lemery. After a long and useful 
life the ancient Greek theory was becoming unequal to the 
strain of advancing with the march of knowledge, and soon we 
shall find it written, 'a new king reigned in his stead'. 

It was the Irishman Boyle who first remorselessly exposed the 
deficiencies of the old 'principles' and thus, in effect, founded 
the modern science of chemistry. The Hon. Robert Boyle was 
born in 1627 at Lismore Castle in Munster. At seventeen years 
of age he went to Oxford, where he began the study of natural 
philosophy, which was to occupy him till his death in 1691. By 
the reckoning of time he was a contemporary of Lemery, but 
Lemery was among the last of the old school while Boyle was 
the first of the new. It is with another contemporary, namely 
Sir Isaac Newton, that Boyle may more properly be compared; 
for although his work did not receive the immediate support 
accorded to that of Newton he nevertheless provided the philo- 
sophical system that has ever since guided the path of 
chemistry. His scientific writings cover a wide range and were 
by no means confined to chemistry, although it is in the latter 
province that the effect of his genius was most beneficially felt. 
Greatest, perhaps, in constructive work as a physicist, his con- 

134 Robert Boyle 

tributions to chemistry were a searching and relentless criticism 
of prevailing theories and a rigorous insistence upon the prin- 
ciples of scientific method formulated, a few years previously, 
by Francis Bacon. His most famous discovery was that of the 
law which describes the behaviour of gases under varying 
pressures, and which still bears his name. Boyle's style is virile 
and precise, and reflects his mental attributes of clear thinking 
and logical deduction. He is seen at his best in his demolition 
of the Aristotelian ' elements' and the Paracelsan * principles', in 
place of which he substituted that definition of an element which 
is now universally adopted. Let us hear him first on the defects 
of the Paracelsans and their 'salt, sulphur, and mercury': 

I might begin [he says] with taking notice of the Obscurity of 
those Principles [i.e. sulphur, mercury, and salt] which is no small 
defect in Notions whose proper office it should be to conduce to the 
illustration of others. For, how can that facilitate the understand- 
ing of an obscure Quality or Phaenomenon which is itself scarcely 
intelligible, or at least needs almost as much explanation as the 
thing 'tis designed and pretended to explicate ? Now a man need 
not be very conversant in the writings of Chymists to observe, in 
how Laxe, Indefinite, and almost Arbitrary Senses they employ the 
Terms of Salt, Sulphur and Mercury ; of which I could never find 
that they were agreed upon any certain Definitions or settled 
Notions; not onely differing Authors, but not unfrequently one 
and the same, and perhaps in the same Book, employing them in 
very differing senses. But I will not give the Chymists any rise to 
pretend, that the chief fault that I find with their Hypothesis is, 
but verbal ; though that itself may not a little blemish any Hypo- 
thesis, one of the first of whose Requisites ought to be Clearness. 
. . . Methinks a Chymist, who by the help of his Tria Prima, takes 
upon him to interpret that Book of Nature of which the Qualities 
of bodies make a great part, acts at but a little better rate than he, 
that seeing a great book written in a Cypher, whereof he were 
acquainted but with three Letters, should undertake to decypher 
the whole piece. ... I must not forget to take notice, that some 
learned modern Chymists would be thought to explicate divers of 
the changes that happen to Bodies in point of Odours, Colours, etc. 
by saying that in such alterations the Sulphur or other Hypostatical 

Robert Boyle 135 

Principle is introverted or extraverted, or, as others speak, inverted, 
But I confess, to me these seem to be rather new terms than real 
explications. . . . 

Thus, dear Pyrophilus, I have laid before you some of the chiei 
Imperfections I have observed in the vulgar Chymists' Doctrine oJ 
Qualities. . . . And as my objections are not taken from the 
Scholastical subleties nor the doubtful speculations of the Peri- 


pateticks or other Adversaries of the Hermetick Philosophy, bu 
from the nature of things and from Chymical experiments them- 
selves ; so I hope, if any of your Spagyrical friends have a minde tc 
convince me, he will attempt to doe it by the most proper way 
which is, by actually giving us clear and particular explications. 

The supporters of the Aristotelian elements fare no better ai 
his hands ; in fact, all the older chemists, he says, in their searches 
after truth, are not unlike the navigators of Solomon's Tarshisl: 
fleet, who brought home from their long and tedious voyage* 
not only gold, and silver, and ivory, but apes and peacocks too 
for some of the chemical theories either, like peacocks' feathers 
make a great show but are neither solid nor useful, or else, like 
apes, if they have some appearance of being rational, an 
blemished with some absurdity or other, that, when they an 
attentively considered, make them appear ridiculous. 

136 Robert Boyle 

Boyle tells us that after he had gone through the common 
operations of chemistry and had begun to make some serious 
reflections upon them, he thought it was a pity that instruments 
that might prove so serviceable to the advancement of natural 
philosophy should not be more studiously and skilfully made 
use of to so good a purpose. Chemistry, he felt, ought not to be 
a mere handmaid to medicine (as the iatrochemists maintained) 
or a slave to the search after transmutation (as the alchemists 
averred), but a natural philosophy, a systematic investigation of 
nature with the object of the advancement of knowledge. 

I saw, indeed, that divers of the Chymists had by a diligent and 
laudable employment of their pains and industry, obtained divers 
Productions, and lighted on several Phaenomena considerable in 
their kind, and indeed more numerous, than, the narrowness and 
sterility of their Principles considered, could be well expected. But 
I observed too, that the generality of those that busie themselves 
about Chymical Operations; some because they practise Physick; 
and others because they either much wanted, or greedily coveted 
money, aimed in their Trials but at the Preparation of good 
Medicines for the humane body, or to discover the ways of curing 
the Diseases or Imperfections of Metals, without referring their 
Trials to the advancement of Natural Philosophy in general; of 
which most of the Alchymists seem to have been so incurious; 
that not onely they did not institute Experiments for that purpose, 
but overlookt and despis'd those undesign'd ones that occur 'd to 
them whilst they were prosecuting to preparation of a Medicine, 
or a Transmutation of Metals. The sense I had of this too general 
omission of the Chymists, tempted me sometimes to try, whether 
I could do any thing towards the repairing of it by handling 
Chymistry, not as a Physician, or an Alchymist, but as a meer 
Naturalist, and so by applying Chymical Operations to Philosophical 
purposes. And in pursuance of these thoughts, I remember I drew 
up a Scheme of what I ventured to call a Chymia Philosophica, not 
out of any affectation of a splendid Title, but to intimate, that the 
Chymical Operations, there treated of, were not directed to the usual 
scopes of Physicians, or Transmuters of Metals, but partly to illus- 
trate or confirm some Philosophical Theories by such Operations ; 
and partly to explicate those Operations by the help of such Theories. 

Robert Boyle 137 

Boyle's masterpiece was his great work The Sceptical Chymist, 
first published at London in 1661. Here, in the form of a 
dialogue between Themistius, who represents the older view, and 
Carneades, the spokesman of Boyle himself, the modern con- 
ception of an element is clearly expressed while previous ones 
are exploded. Themistius is allowed to give a very fair and just 
exposition of the theories of the peripatetics and Paracelsans, 
but Carneades seizes on their weak points with unerring acumen 
and demonstrates with cold logic how profoundly unsatisfactory 
Themistius 's arguments prove to be when closely examined. 
The chemists' typical 'proof that substances consist of fire, air, 
earth and water lay in pointing out the fact that when a piece of 
wood is burnt (a) fire appears, (6) water boils and hisses from 
the ends of the burning wood, (c) smoke ascends into the air, 
where it vanishes, thus showing itself to be of the same nature, 
and (d) an earthy ash is left. Boyle pertinently inquires what 
proof there is that the fire, air, earth and water really are present 
in wood before combustion, and also demands evidence for 
assuming that the four 'elements' are actually 'simpler' than the 
original wood. Obtaining no convincing answer he sums up as 
follows : 

Since, in the first place, it may justly be doubted whether or no the 
fire be, as chymists suppose it, the genuine and universal resolver 
of mixt compound bodies ; 

Since we may doubt, in the next place, whether or no all the 
distinct substances that may be obtained from a mixt body by the 
fire were pre-existent there in the formes in which they were 
separated from it ; 

Since also, though we should grant the substances separable 
from mixt bodies by the fire to have been their component in- 
gredients, yet the number of such substances does not appear the 
same in all mixt bodies; some of them being resoluble into more 
differing substances than three; and others not being resoluble 
into so many as three ; 

And since, lastly, those very substances that are thus separated 
are not for the most part pure elementary bodies, but new kinds of 
mixts ; 

138 Robert Boyle 

Since, I say, these things are so, I hope you will allow me to 
inferr, that the vulgar experiments (I might perchance have added, 
the arguments too) wont to be alledged by chy mists to prove, that 
their three hypostatical principles do adequately compose all mixt 
bodies, are not so demonstrative as to induce a wary person to 
acquiesce in their doctrine, which, till' they explain and prove it 
better, will by its perplexing darkness be more apt to puzzle than 
satisfy considering men, and will to them appear incumbered with 
no small difficulties. 

There is, he says, no valid reason for limiting the number of 
the elements to four, as the Aristotelians do, or to three, like the 
Paracelsans, or indeed to any particular, preconceived number: 
And if according to this notion we allow a considerable number of 
differing elements, I -may add, that it seems very possible, that to 
the constitution of one sort of mixt bodies two kinds of elementary 
ones may suffice (as I lately exemplified to you, in that most durable 
concrete, glass), another sort of mixts may be composed of three 
elements, another of four, another of five, and another perhaps of 
many more. So that according to this notion, there can be no 
determinate number assigned, as that of the elements, of all sorts 
of compound bodies whatsoever, it being very probable that some 
concretes consist of fewer, some of more elements. Nay, it does not 
seem impossible, according to these principles, but that there may 
be two sorts of mixts, whereof the one has not any of all the same 
elements as the other consists of; as we oftentimes see two words, 
whereof the one has not any of the letters to be met with in the 

Finally, having accomplished his destruction of the Four 
Elements and the tria prima, he completes his work by stating 
his own view of an element as it should be conceived in chemistry : 
I mean by elements, as those chymists that speak plainest do by 
their Principles, certain primitive and simple, or perfectly 'un- 
mingled bodies; which not being made of any other bodies, or of 
one another, are the ingredients of which all those called perfectly 
mixt bodies are immediately compounded, and into which they are 
ultimately resolved. ... I must not look upon any body as a true 
principle or element, which is not perfectly homogeneous, but is 
further resolvable into any number of distinct substances. 



Doubts & Paradoxes , 

Touching the 

Commonly call'd 



As they, are wont to be Propos'd and 

Defended by the Generality of 


!Whereunto is prsmis'dPart of another Difcourfc 
relating to the fame Subject. 

B Y 
The Honourable ROBERT tOTLE, Efqj 


printed by J* Cattvell for J* Crookt, and are to be 
Sold at the Ship in St JtAvfr Church-Yard* 
D Cl. -JT /. 

Fig. 39 

140 Robert Boyle 

In other words, chemists should regard as elementary all those 
substances that they have not yet been able to split up into two 
or more constituents, and should not limit themselves by any 
preconceived notions of the number of these elements. If a sub- 
stance is undecomposable it is to be considered an element, and 
it will retain that title for just so long as it withstands the efforts 
of chemists to decompose it. It will be seen that Boyle's defini- 
tion of an element was purely empirical, and that instead of 
postulating any definite number of elements he is content to 
investigate the subject experimentally and so to find out how 
many there actually are. This attitude is so much our own that 
we find it difficult to realize the revolutionary character that it 
presented to Boyle's contemporaries. It made, indeed, little 
immediate progress ; Boyle himself afterwards complained : 

I thought the rousing stile I sometimes wrote in, might prove no 
unhopefull way to procure somewhat considerable from those 
great Masters, and orders of Chymicall Arcana, that must be 
provok'd before they will come out with them ; as the sea is observ'd 
not to give us one of its preciousest treasures, Ambergreece; till it 
have been agitated by winds and storms. 

He was disappointed at the lack of controversy and discussion 
that he had hoped to arouse, but, on looking back, we can see 
that from the date of the publication of The Sceptical Chymist 
the Aristotelian elements became obsolete. One reason, at least, 
for the lack of discussion was the impossibility of answering 
Boyle's arguments. 

Boyle himself was unable to evolve experimental methods of 
deciding whether or not a given substance is to be considered an 
element; that advance was left for the great Lavoisier, whose 
acquaintance we shall soon make. It is, however, interesting 
to compare Lavoisier's own statement on the nature of the 
chemical elements, made in 1789, with that which Boyle had 
expressed a century earlier. Lavoisier says : 

It is very remarkable, notwithstanding the number of philosophical 
chemists who have supported the doctrine of the four elements, 
that there is not one who has not been led by the evidence of facts 

Robert Boyle 141 

to admit a greater number of elements into their theory. The first 
chemical authors, after the revival of letters, considered sulphur 
and salt as elementary substances entering into the composition of 
a great number of substances ; hence instead of four, they admitted 
the existence of six elements. Becher assumes the existence of 
three kinds of earth; from the combination of which, in different 


proportions, he supposed all the varieties of metallic substances to 
be produced. Stahl gave a new modification to this system; and 
succeeding chemists have taken the liberty to make or to imagine 
changes and additions of a similar nature. All these chemists were 
carried along by the genius of the age in which they lived, being 
satisfied with assertions instead of proofs; or, at least, often 
admitting as proofs the slightest degrees of probability, unsup- 
ported by that strictly rigorous analysis which is required by 
modern philosophy. 

All that can be said upon the number and nature of elements is, 
in my opinion, confined to discussions entirely of a metaphysical 
nature. The subject only furnishes us with indefinite problems, 

142 Robert Boyle 

which may be solved in a thousand different ways, not one of which, 
in all probability, is consistent with nature. I shall, therefore, only 
add upon this subject, that if, by the term elements, we mean to 
express those simple and indivisible atoms of which matter is 
composed, it is extremely probable that we know nothing at all 
about them; but, if we apply the term elements or principles of 
bodies, to express our ideas of the last point which analysis is 
capable of reaching, we must admit, as elements, all the sub- 
stances into which we are able to reduce bodies by decomposition. 
Not that we are entitled to affirm, that these substances which we 
consider as simple, may not themselves be compounded of two, or 
even of a greater number of more simple principles; but since 
these principles cannot be separated, or rather since we have not 
hitherto discovered the means of separating them, they act with 
regard to us as simple substances, and we ought never to suppose 
them compounded until experiment and observation has proved 
them to be so. 

And lastly, to show how much alive Boyle's idea still is, we 
may quote the following words from J. W. Mellor's Compre- 
hensive Treatise on Inorganic and Theoretical Chemistry (1922) : 
The definition of an element is not founded upon any intrinsic 
property of the elements, but rather upon the limited resources of 
the chemist. To find if a given substance is an element or com- 
pound, it is usual to assume that it is a compound and then to 
apply all known methods for resolving compounds into simple 
substances. If the methods fail to effect a decomposition, the 
substance is said to be an element. ... In fine, element is a con- 
ventional term employed to represent the limit of present-day 
methods of analysis or decomposition. We may, therefore, 
summarize these ideas in the definition : An element is a substance 
which, so far as we know, contains only one kind of matter. To say 
the substances we call elements cannot be decomposed may be 
regarded as an unwarranted reflection on the powers of our 

We have not yet bidden farewell to Boyle, whom we shall meet 
again in succeeding pages ; but in this place it may be recalled 
that he it was who introduced into Oxford the first regular 
teacher of practical chemistry, viz. 'the noted chemist and Rosi- 

Becher and Stahl 143 

crucian, Peter Sthael of Strasburgh in Royal Prussia, a Lutheran, 
a great hater of women, and a very useful man'. Boyle engaged 
Sthael as his assistant, but allowed him to have pupils, among 
whom was the philosopher John Locke. Locke, we are told, 
was 'a man of turbulent spirit, clamorous and never contented. 
The club [class] wrote and took notes from the mouth of their 
master, who sat at the upper end of a table ; but the said J. Lock 
scorned to do it ; so that while every man besides of the club 
were writing, he would be prating and troublesome.' However, 
says Dr. Gunther, a few years later we find him writing to Boyle, 
'I find my fingers still itch to be at it' (experiments in chemistry). 

37. Becher and Stahl 

IT has already been mentioned that Boyle's work evoked little 
immediate response, coming to full fruition only a century later. 
The explanation must be sought mainly in the fact that chemists 
became deeply engrossed in a theory of combustion, which 
occupied the attention of practically all the best minds of the 
eighteenth century to the virtual exclusion of everything else. 
Comprehensive theories are very seldom perhaps never the 
work of one man, as we shall have many opportunities to realize. 
A suggestion here, another there, a casual remark, an old hypo- 
thesis, such are the materials that the genius takes and moulds 
into a new and better form. Nowhere do we find this more 
clearly demonstrated than in the history of theories of combus- 
tion. For centuries combustion was regarded as a decomposition 
of the burning substance into its constituents, so that only com- 
pound bodies could be combustible. On the sulphur-mercury 
theory of metals, elaborated by Jabir, the combustion of a metal 
was explained by supposing the loss of its sulphureous constituent. 
Advancing knowledge soon rendered this primitive theory un- 
tenable, and even among the chemists of Islam, as well as in the 
thirteenth and fourteenth centuries in Europe, the combusti- 
bility of a substance was assigned to the presence in it of an oily 
constituent. Sulphur, from its greasy feel and from its oily 
appearance when molten, was believed to contain a high per- 

144 Becher and Stahl 

centage of this oil, and one of the Latin works ascribed to Jabir 
goes so far as to say that sulphur is merely 'an oily fatness of the 
earth'. A metal, therefore, containing sulphur as an essential 
constituent, would, ipso facto, be combustible. The residue left 
after the calcination or burning of a metal was regarded as the 


mercurial constituent contaminated with more or less earthy 

This vague theory of combustion, with various modifications 
in detail, persisted up to the middle of the seventeenth century. 
The theory favoured by Paracelsus, that there was a third, saline, 
constituent of bodies, did not essentially change ideas of com- 
bustion it remained the generally accepted belief that any- 
thing which would burn contained an oily, sulphureous prin- 
ciple : ubi ignis et color ibi sulphur. Such was the state of affairs 
when Johann Joachim Becher (1635-82) in 1669 published his 
Acta Laboratorii Chymici Monacensis, seu Physica Subterranea, 

A6lorum Laboratori'i 

Chyraici Monaccnfis, 



Quorum Prior profun- 

dam fubterraneorumgcnefin,nccnon 

admirandatH Globi terr- aquc- aerci fuper 

&/iibtcrranci.fabricam , Pofltrior fpccialcm fubtcrra* 

neorum Naturam , refolutionem in partes partiumq; 

proprictates exponit>acccfferant fiib fincm *_5\fiHc 

bjpotkefcs feu mixtioncs Chymicx , ante hac nun* 

4quam vifir , omnia, plusquam imllc experiments fta- 

biiica, fumptibus&permiffii^r^j/&w/ ElettorU 

B4F4f/^&c. 'Domini fui clement tfiimi 

elabocavic &publicavic 



3Med.D. Sacrae C<*ftr. Majeftatu Conjll'ut- 

riw , nee non SercniJJtmi B#vari* ElcHorif 

AuU Medic'tt. 




Fig. 42 

2613 4 

146 Becher and Stahl 

in which he promulgated the theory that in the hands of his 
pupil, Stahl, finally assumed such imposing dimensions. 

According to Becher, all minerals were composed of three 
constituents, in varying proportions terra pinguis, terra mercu- 
rialis, and terra lapida. The first two obviously correspond to 
the old sulphur and mercury, while the third is parallel with 
the saline constituent. Every combustible substance Becher 
believed to contain terra pinguis y which was lost on com- 
bustion. * Metals', he says, * contain an inflammable principle 
which by the action of fire goes off into the air ; a metal calx is 
left', that is, its terra lapida and terra mercurialis. Combustion 
is therefore a disintegration of the burning body and the loss of 
its more volatile constituent. 

It will be seen that Becher 's theory was only a re-expression 
of older ideas in language a little less vague. His terra pinguis is 
the inflammable earth, the fiery oil, and the burning sulphur of 
the ancients. Nevertheless, his arguments and illustrations were 
so forcible that they carried conviction where before there had 
been doubt, and, when elaborated and extended by Georg 
Ernst Stahl (1660-1734), Becher's form of the theory won the 
allegiance of practically all chemists. 

Stahl re-edited the Physica Subterranea in 1702, and added 
a work of his own, the Specimen Becherianum, in which he ex- 
pressed his views of combustion. The materia ignis of com- 
bustible bodies he called phlogiston ('burnt', from </>Aoyiiv to 
inflame), thus giving his theory the name by which it has 
been known ever since. Stahl did not regard phlogiston as 
fire itself, but rather as the material of fire materia out prin- 
cipium ignis, non ipse ignis. It is contained in all combustible 
bodies as an essential constituent, and is given up to the air on 
combustion. It becomes appreciable to our senses only when it 
leaves the body with which it was combined, and appears in the 
form of fire with its accompaniments of light and heat. The 
richer a substance is in phlogiston, the more easily it may be 
burnt, and the more ready it will be to give up phlogiston to 
substances that do not already possess it, or possess it only in 

Becher and Stahl 147 

small quantity. As for the actual process of combustion, this is 
merely a liberation of phlogiston from the body that is being 

Now practically all metals may be converted into an ash by 
means of heat, even though they may not be inflammable in the 
ordinary sense of the word ; the metallic ashes were known as the 


calces of the metals and the process was called calcination. 
According to Stahl, the calcination or burning of a metal was to 
be explained in the same way as the combustion of any other 
combustible body, namely, as a loss of phlogiston. Metals, in 
short, were to be considered as compound bodies, each com- 
posed of two constituents : phlogiston and calx. Different metals 
naturally have different calces, but the dual composition is 
common to all metals. Oil, charcoal, fats, &c., which burn away 
almost completely and leave little residue, are, from that very 
property, extremely rich in phlogiston. Hence, if a metallic calx 

L 2 

148 Becher and Stahl 

is heated with charcoal, for instance, one might expect the 
charcoal to give up some of its phlogiston to the calx, thus re- 
converting the latter into the metal. The fact that metallic 
calces can thus be 'reduced' to metal by heating with charcoal 
had, of course, been known for centuries, and at length a reason- 
able hypothesis was advanced to explain it. 

Let us take a definite example of the phenomenon and hear 
how it was explained by R. Watson, Professor of Divinity (!) in 
the University of Cambridge : 

Lead, it has been observed, when melted in a strong fire, burns 
away like rotten wood ; all its properties as a metal are destroyed 
and it is reduced to ashes. If you expose the ashes of lead to 
a strong fire, they will melt; but the melted substance will not be 
a metal ; it will be a yellow or orange coloured glass [litharge] . If you 
pound this glass and mix it with charcoal dust, or if you mix the 
ashes of the lead with charcoal dust, and expose either mixture to 
a melting heat, you will obtain, not a. glass, but a metal, in weight, 
colour, consistency, and every other property the same as lead. . . . 
The ashes of lead melted without charcoal become glass ; the ashes 
of lead melted with charcoal become a metal \ the charcoal then 
must have communicated something to the ashes of lead, by which 
they are changed from a glass to a metal ; charcoal consists but of 
two things, of ashes, and of phlogiston ; the ashes of charcoal, though 
united with the ashes of lead, would only produce glass; it must 
therefore be the other constituent part of charcoal, or phlogiston, 
which is communicated to the ashes of lead, and by an union with 
which the ashes are restored to their metallic form. The ashes of 
lead can never be reduced to their metallic form, without their 
being united with some matter containing phlogiston, and they 
may be reduced to their metallic form, by being united with any 
substance containing phlogiston in a proper state. 

The phlogiston theory, then, offered a rational explanation of 
the formation of metallic calces and of the reduction of the latter 
to metals : but it did more. Like every scientific theory worthy 
of the name it soon proved to be applicable to facts with which 
at first it seemed completely unconnected, and by bringing them 
all to a common denominator it achieved the earliest great 

Becher and Stahl 149 

synthesis of chemical philosophy. Thus the experimental facts 
(a) that when sulphur is burnt under suitable conditions it yields 
sulphuric acid, and (b) that by the action of charcoal upon 
sulphuric acid sulphur can be regenerated, were simply and con- 


sistently explained by assuming that sulphur is composed of 
sulphuric acid and phlogiston. Upon burning sulphur the 
phlogiston is lost and the acid remains, but when the acid is 
heated with charcoal a substance rich in phlogiston it once 
more combines with phlogiston to form sulphur. Again, if zinc 
is dissolved in dilute sulphuric acid a colourless inflammable 
gas [hydrogen] is evolved and a solution of white vitriol remains. 
The inflammable gas was regarded as practically pure phlogis- 

150 Troublesome Facts 

ton, and the reaction was explained by supposing that the acid 
split up the zinc into 'phlogiston' (which was evolved) and zinc 
calx, the latter dissolving in the acid to form the white vitriol. 
A logical deduction from this hypothesis was that if zinc were 
first burnt, so removing its phlogiston, the residual zinc calx 
should dissolve in dilute sulphuric acid, to yield a solution of 
white vitriol without evolution of the inflammable gas. Experi- 
ment shows that this deduction is correct, for the reaction takes 
place exactly as indicated. 

Further, it follows from the phlogiston theory that if a metallic 
calx is heated in the above-mentioned inflammable gas, the 
metal ought to be regenerated : a deduction which once more is 
in perfect agreement with the experimentally established fact. 
And lastly, the facts that a combustible substance will not burn 
in a vacuum, and that its flame is soon extinguished in a limited 
supply of air, were explained by assuming that a medium is 
necessary to absorb phlogiston, just as a sponge absorbs water. 

To the original hypothesis of Becher and Stahl addition after 
addition was made, until a large and complex theoretical system 
was constructed and practically every known type of chemical 
reaction found a more or less satisfactory explanation. The chief 
protagonist of the adult theory was the French chemist Macquer, 
who devoted a lengthy article to phlogiston in his Dictionnaire 
de Chimie (second edition, 1778). There is, however, no need for 
us to follow all the intricacies of his exposition, the main points 
of the theory having remained unchanged from the time of their 
formulation by Stahl. It will be more profitable for us to turn 
next to some of the difficulties that the phlogistians had to face 
and to witness the growth of those intractable facts that after- 
wards led to a revolution in chemical theory. 

38. Troublesome Facts 

' NOTWITHSTANDING all that perhaps can be said upon the 
subject/ admits Watson, 'I am sensible the reader will be still 
ready to ask what is phlogiston!' Replying to this question he 
says, 'You do not surely expect that chemistry should be able to 

Troublesome Facts 151 

present you with a handful of phlogiston, separated from an 
inflammable body ; you may just as reasonably demand a handful 
of magnetism, gravity, or electricity to be extracted from 
a magnetic, weighty, or electric body ; there are powers in nature, 
which cannot otherwise become the objects of sense, than by the 
effects they produce, and of this kind is phlogiston.' It may be 
doubted whether this explanation satisfied all of Watson's 
readers, or whether, even, it would have satisfied Stahl himself; 
the latter, indeed, definitely regarded phlogiston as a material 
substance though of a very subtle nature, invisible, in constant 
and rapid spiral motion and capable of penetrating the densest 
substances. We begin to see that the question, 'What is phlogis- 
ton?' was a very pertinent one, and that the reply given was 
rather an evasion than an answer. 

A more serious difficulty was that during calcination metals 
undergo an increase in weight. This fact had been known for 
a great many years, for it is mentioned by Jabir in the eighth 
century, by Eck de Sultzbach in 1489, and by Cardanus in 1553. 
Attention had been specifically directed to it by Jean Rey in 
1630, who remarks in his Essays that some eminent personages 
had observed with astonishment that tin and lead increase in 
weight when they are calcined, and that he had been asked by 
the Sieur Brun, Master Apothecary in Bergerac, to furnish him 
with an explanation of this phenomenon. Brun had placed 2 Ib. 
6 oz. of fine English tin in an iron vessel and heated it strongly 
on an open furnace for the space of six hours with continual 
agitation and without adding anything to it. At the close of the 
operation he recovered 2 Ib. 13 oz. of a white calx, which filled 
him with amazement and with a desire to know whence the 7 oz. 
of surplus had come. Rey considered carefully all the conflicting 
hypotheses that had been advanced in explanation, and showed 
that they were untenable. He then attempted to show that 
the only hypothesis in accordance with the observed facts 
was 'that this increase in weight comes from the air, which in 
the vessel had been rendered denser, heavier, and in some 
measure adhesive, by the vehement and long-continued heat of 

152 Troublesome Facts 

the furnace : which air mixes with the calx (frequent agitation 
aiding) and becomes attached to its most minute particles'. 

Rey meets the objection that, the amount of air available being 
practically unlimited, there should be no limit to the increase in 
weight of a metal upon calcination, by saying that Nature is 
scrupulous to stop at the bounds she has once prescribed her- 
self. The calx is in this condition : the condensed air becomes 
attached to it, and adheres little by little to the smallest of its 
particles: thus its weight increases from the beginning to the 
end, but when all is saturated it can take up no more. 'Do not 
continue your calcination in this hope: you would lose your 
labour/ He concludes with 

another objection which might be raised. Why do not all other 
calces and ashes made by the force of fire increase in weight as well 
as the calx of tin and of lead ? What privileges have these over the 
others? I answer that the things calcined or incinerated are of 
different nature. Some have much exhalable and evaporable 
matter, or much sulphur and mercury, which the fire expels to the 
end. Here there is much diminution and little ash, which cannot 
attach to itself as much of the air condensed by fire as even to make 
up for the decrease. Others have little exhalable and evaporable 
matter, or little sulphur and mercury : consequently there is little 
diminution, and much ash . . . which attracts so much of the 
condensed air, that not only is the diminution made good, but the 
weight increases largely in addition. 

Lemery was equally puzzled by the increase in weight that 
occurs during the calcination of a metal. 'In the calcination of 
lead and of several other substances/ he says in his Cours de 
Chymie (1675), * there occurs an effect which well deserves that 
some attention should be paid to it ; it is that although by the 
action of the fire the sulphureous or volatile parts of the lead are 
dissipated, which should make it decrease in weight, neverthe- 
less after a long calcination it is found that instead of weighing 
less than it did, it weighs more/ 

This was indeed an awkward fact for the Theory of Phlogis- 
ton. Surely, one might argue, if phlogiston is lost when a metal 

Troublesome Facts 153 

is calcined, the calx ought to weigh less than the original metal. 
The actual fact was widely known Stahl himself knew it and 
it had been established beyond dispute. To us, it would have 
rendered the phlogiston theory untenable from the very start, 
but the phlogistians were wholly unperturbed. Some of them 
followed Stahl's lead in regarding an alteration in weight during 
a chemical change as an unimportant detail that might be 
neglected ; a course of action which may serve to remind us that 
the quantitative age of chemistry had not yet arrived. In those 
days, moreover, the distinction between weight and density was 
not so clear as it afterwards became, so that, taking a sympathetic 
view, we can perhaps understand Stahl's attitude. Other 
chemists adopted the standpoint that the fact was admittedly 
inexplicable, but that the phlogiston theory explained so many 
other facts, and explained them so well, that the solution of the 
matter might safely be left to the future. Still others, such as 
Venel and Guyton de Morveau, sought escape from the diffi- 
culty by ascribing to phlogiston a negative weight. 'Phlogiston,' 
said Venel in his course of chemistry at Montpellier, 'is not 
attracted towards the centre of the earth, but tends to rise; 
thence comes the increase in weight in the formation of metallic 
calces and the diminution in weight in their reduction'! Com- 
ment upon this over-ingenious suggestion is unnecessary. 

Boyle himself had been attracted to the problem of the nature 
of the changes that occur during the calcination of metals. 
He calcined weighed quantities of copper, lead, tin and other 
metals, and noted that in every case there was an increase in 
weight. In one experiment, 

two ounces of filings of tin were carefully weighed and put into 
a little retort, whose neck was afterwards drawn slender to a very 
small apex ; then the glass was placed on kindled coals, which drove 
out fumes at a small orifice of the neck, for a pretty while. After- 
wards the glass, being sealed at the apex, was kept in the fire for 
above two hours, and then being taken off, was broken at the same 
apex: whereupon I heard the external air rush in, because, when 
the retort was sealed the air within it was highly rarefied. Then 

1 54 Mayow 

the body of the glass being broken, the tin was taken out, consisting 
of a lump, about which there appeared some grey calx, and some 
very small globules, which seem to have been filings melted into 
that form. The whole weighed two ounces and twelve grains. 

Boyle explained the increase in weight by assuming that the 
metal had absorbed heat, which he imagined to be a material 
substance possessing weight. It has been erroneously stated 
that Boyle's explanation of calcination formed the basis of the 
phlogiston theory, but that this statement is incorrect is obvious 
in view of the facts that (i) the phlogiston theory is merely 
i development of more ancient views on combustion, and (2) on 
the phlogiston theory combustion was a decomposition, whereas 
according to Boyle it was a combination: Boyle, for example, 
:onsidered lead calx to be lead plus heat, while Becher and 
Stahl regarded it as lead minus phlogiston. 

We must now consider a further difficulty that confronted 
:he phlogistians, viz. the necessity of air for combustion. The 
solution which they offered, it will be remembered, was that the 
iir provided a medium in which the phlogiston could be 
ibsorbed ; in the absence of such a medium phlogiston could not 
3e given off from a combustible body, which would consequently 
3e unable to burn. Similarly, when a given quantity of air was 
saturated with phlogiston it would naturally be unable to 
support combustion. One of the facts that these suggestions 
were intended to explain had been known from time immemorial, 
lamely, that substances will not burn indefinitely in a limited 
volume of air, while the other that substances will not burn in 
i vacuum had been established by Boyle and was now common 
3roperty. The hypothesis advanced by the phlogistians was not 
he only one put forward, and as the others are of importance 
,hey may be briefly described. 

39. Mayow 

WE saw that Rey had supposed the increase in weight on calcina- 
ion of a metal to be caused by the condensation of air upon the 
^articles of calx, an idea which at first sight appears to fore- 

Mayow 155 

shadow the theory we now hold. Reflection will, however, show 
us that Rey imagined the calx to be formed first, in some way 
that he does not explain, and only afterwards to absorb the 
condensed air. There is thus a vital difference between his 
hypothesis and the modern theory. A like remark applies to the 

Pig- 45 

work of Robert Hooke (1635-1703), who suggested that the 
combustion of a substance when heated with saltpetre is similar 
in essentials to its combustion in air : he regarded combustion as 
a loss of the sulphureous principle which was taken up by the air 
in the one case and by the saltpetre in the other. 

The researches of John Mayow deserve closer attention, since 
this remarkable man has been held to have 'anticipated the work 
of Lavoisier (1775) by more than a century'. Mayow was born 
in London in 1643, went to Wadham College, Oxford, in 1658, 

156 Mayow 

and became a Fellow of All Souls in 1660. In 1675 he settled in 
Bath as a practising physician, devoting his leisure hours to 
scientific research, on the results of which he was elected a Fellow 
of the Royal Society in 1678. A few months later, on a visit to 
London, he died 'in an apothecarie's house bearing the sign of 
the Anker in York Street, Covent Garden, having a little before 
been married not altogether to his content'. 

Like Hooke, Mayow emphasized the similarity between com- 
bustion in air and combustion in saltpetre, but suggested that 
probably air and saltpetre contain a common 'spirit* necessary 
to combustion; this he called the nitro-aerial spirit. He remarks 
that it has 

to be admitted that something aerial, whatever it may be, is 
necessary to the production of any flame a fact which the ex- 
periments of Boyle have placed beyond doubt, since it is established 
by these experiments that a lighted lamp goes out much sooner in 
a glass that contains no air than it does in the same when filled with 
air a clear proof that the flame goes out . . . because it is deprived 
of its aerial food. ... In the second place, it would be reasonable to 
suppose that the igneous particles of air necessary to the support of 
all flame reside in sal nitrum and constitute its more active and 
fiery part, for it is to be noted that nitre mixed with sulphur 
deflagrates readily enough in a glass which does not contain air. 

Mayow also observed the increase in weight during calcina- 
tion and the decrease in volume which a limited quantity of air 
undergoes when a candle is burnt in it. The former observation 
he explains by assuming that the metal unites with nitro-aerial 
particles, and the latter by the loss of nitro-aerial particles from 
the air. Superficially, these explanations seem astonishingly like 
our own, if we substitute 'oxygen* for 'nitro-aerial particles'; 
and Mayow has thus been credited with the great discovery 
usually attributed to Lavoisier. 

Professor J. B. Cohen, however, in 1901 pointed out that 
Mayow's nitro-aerial spirit differs essentially from the modern 
oxygen, in that (a) although nitro-aerial particles are present in 
the air they are not a part of it ; (b) the sun's rays are imagined 


158 Pneumatic Chemistry 

to be a chaos of nitro-aerial particles; (c) metallic iron, which 
forms sparks when struck, therefore contains nitro-aerial 
particles ; (d) the latter can be annihilated ; (e) they give rise to 
heat if set in motion ; (/) they appear to be confused with the red 
fumes given off when nitric acid is heated. The conclusion to be 
drawn is that although Mayow appreciated the necessity of air 


for combustion, and the similarity between combustion in air 
and deflagration in nitre, he had no real conception of the true 
nature of burning or of the composition of the air. The solution 
of these problems is the honour of Lavoisier and of Lavoisier 

40. Pneumatic Chemistry 

THE age of phlogiston might equally well be called the age of 
pneumatic chemistry, for it was during the period in which the 
brilliant theory of Stahl reached its zenith, that many of the 
common gases were first discovered, collected and investigated. 
One of the most familiar objects of a modern chemical laboratory 

Pneumatic Chemistry 159 

is the pneumatic trough, at which gases are collected by the 
displacement of water or, less frequently, mercury. So simple is 
the device that, having once seen it in use, we are apt to take it 
purely as a matter of course and rarely regard it as a supreme 
achievement of the inventive genius. Perhaps this indifference 
is only natural, but what an immensity of labour lies behind the 


trite instruction of the text-book: 'Collect the gas over water at 
the pneumatic trough'! Indifference before even the dullest 
chemical experiment cannot survive a knowledge of the work 
which made that experiment possible. Every chemical we use, 
every piece of apparatus we take, and every experiment we per- 
form, hide a romance. Who, for instance, automatically selecting 
a cork to stopper his flask, gives a thought to the origin of that 
admirably effective contrivance ? It comes as a surprise to find 
that the use of corks for closing bottles is not yet 300 years old ; 
it is said to have been introduced by the Benedictine monk Dom 
Perignon about 1680. Perignon was born in 1638 and became 
Cellarer of the monastery of Hautvillers, not far from Reims. 
As the result of much long and patient observation, he invented 
the wine now universally known as champagne, but was faced 

160 Pneumatic Chemistry 

with the difficulty of preserving its effervescent nature. He finally 
hit upon the idea of closing the bottles with pieces of cork, and 
such was the superiority of this method over all which had gone 
before that the whole world rapidly adopted it. Let us toast 
Dom Perignon's service to chemistry in a glass of his own wine! 

We have already heard of van Helmont's new name, gas, for 
those 'wild, untamable' varieties of matter that resist imprison- 
ment, and of his failure to devise a means of collecting them. 
Boyle was more ingenious. He took a glass flask with a long neck 
and completely filled it with dilute sulphuric acid . He then dropped 
in six iron nails and inverted the flask in a vessel containing 
more of the dilute acid. Bubbles of gas [hydrogen] were formed 
and rose to the top of the apparatus, displacing the acid and soon 
filling the flask. Here was the germ of the pneumatic trough. 

Mayow made a further advance, showing that a gas could be 
transferred from one vessel to another by filling the latter with 
water, inverting it in a trough of water, and bringing the mouth 
of the first vessel, containing the gas, under the mouth of the 
other ; 'care being taken [as he says] that the mouth of neither of 
the glasses is raised above the surface of the water'. He further 
emphasized the importance, in quantitative work, of levelling 
the water inside and outside ajar containing gas, in order to get 
the latter at atmospheric pressure. This he accomplished by 
means of a siphon-tube. 

A few years later Jean Bernouilli (1667-1748) used the 
apparatus illustrated in fig. 48 to demonstrate experimentally the 
fact that the propulsive force of gunpowder is due to the pro- 
duction of gases that, when liberated, occupy a much greater 
space than the powder from which they are formed. 

Another skilful manipulator of gases chiefly air was the 
French physician Moitrel d 'Element, who dwelt in a wretched 
garret in the Rue Saint-Hyacinthe, Paris, towards the beginning 
of the eighteenth century. To relieve his poverty, he gave a 
public course of experiments on air, in which he 'measured air by 
pints', transferring it from one vessel to another in the way 
suggested by Mayow. 

Pneumatic Chemistry 161 

The next improvement was made by the Englishman Stephen 
Hales (1677-1761). In 1724 Hales undertook a comprehensive 
research upon the physiology of plants, and in 1727 published 
his results in a book entitled Vegetable Staticks. Having 


occasion to conduct many experiments with gases in connexion 
with his botanical work, Hales devoted himself to the elabora- 
tion of a suitable technique. He devised several forms of 
apparatus for the purpose, but the most interesting is shown in 
fig. 50 ; it will be at once recognized as our modern pneumatic 
trough in an unusual shape. 

Further development was mainly a matter of detail, though it 
should be mentioned that Boerhaave (1668-1738) measured the 




Pneumatic Chemistry 163 

volume of a gas evolved in a particular reaction by conducting 
the reaction in vacua ^ noting the change in pressure, and correct- 
ing by the then newly-discovered Boyle's Law. With Priestley 
(p. i69)we find the trough in its present-day shape, but Priestley 


had the happy inspiration of substituting, on occasion, mer- 
cury for water, and so made the discovery of several gases 
which, since they are soluble in water, had previously been 

With the recognition of gases as definite species of matter or 
rather as different varieties of 'air* and with the establishment 
of methods of collecting and measuring them, the way was open 
for great progress. Of the five 'makers of chemistry' we are 
are about to meet, four owe their fame chiefly to their work on 

M 2 

[i6 4 ] 

41. Joseph Black 

AMONG the chemists of the middle of the eighteenth century, 
five men tower high above the rest : Guillaume Francois Rouelle 
(1703-70), Joseph Black (1728-99), the Hon. Henry Cavendish 


(1731-1810), Karl Wilhelm Scheele (1742-86), and Joseph 
Priestley (1733-1804). Of these men the last three were stead- 
fast adherents of the phlogiston theory, while Black and Rouelle 
were largely indifferent, devoting themselves to their researches 
and placing their own interpretations upon the results. 

Joseph Black, the son of a Scottish wine-merchant residing at 
Bordeaux, was born in France in 1728. At the age of 1 8 he went 
to Glasgow University, where he had the good fortune to begin 
the study of chemistry under Dr. William Cullen. Cullen, 
though not a great investigator, saw chemistry as a Vast depart- 
ment of the science of nature' rather than as a 'curious and useful 
art', and the lectures he gave on the subject are inspired through- 

Joseph Black 165 

out with the true spirit of scientific method. These lectures 
were never published, but a lucky chance has preserved a 
manuscript copv made by one of Cullen's pupils, 1 from which 


the following passage may be quoted as an example of the 

splendid teaching the young Black received : 

In all our reasonings we are apter to be led into error by assuming 
false premises, than by drawing fallacious conclusions when the 
premises are just. We must therefore in our Chymical Enquiries 
be remarkably accurate in collecting Facts, as it is from these alone 
that a proper System can be deduced. In particular we must guard 
against many Facts that are related in Books of chymistry, as many 
of them are false through a Design to cheat (at least of those that 
we find in the Books of the old Alchymists) and others, where that 
is not the case, Erroneous through Inaccuracy. As an Instance of 
the latter kind Lime water was always said to be strong in propor- 

1 Dr. William Falconer. The manuscript is in the Science Library at 
Clifton College. 

1 66 Joseph Black 

tion to the quantity of Lime that was put into a given quantity of 
water, but Dr. Alston has shewn that one Pound of Limestone 
[i.e. 'burnt limestone' or quicklime] Impregnates 40 of Water as 
strongly as it does 10. 

Those facts that are merely deduced from Theory without the 
Concurrence of Experiment ought not to be admitted : Macquer 
in this way tells us that a Salt is formed of the combination of 
Water and Earth. 

Only such Experiments ought to be depended on, as have been 
often repeated, for there are many which vary remarkably every 
time they are performed either from some difference in the opera- 
tion or the Difficulty we find in subjecting them to the observation 
of our senses, by which means some of the most remarkable 
Phaenomena escape us. This was long the case in making Aether. 
In relating Facts every concurrent Circumstance ought to be 
taken notice of in order to render them as complete as possible. 
This is a thing of the utmost consequence and in general very little 
attended to. 

In 1756 Cullen was called to Edinburgh and Black succeeded 
to the Glasgow professorship. Ten years later Cullen resigned 
the chair of chemistry at Edinburgh, and again Black followed 
him. At Edinburgh he remained until his death in 1799. Great 
as a teacher, Black was no less eminent as an experimenter, and 
although he published only three papers on chemical subjects, 
these were models of accuracy and logic, and may still be read 
with profit. The most important of the three is entitled Experi- 
ments upon Magnesia Alba, Quicklime, and some other Alcaline 
Substances, published in 1756. A modern reprint of it was made 
by the Alembic Club, with a short preface in which it is well 
remarked that 

the paper constitutes a highly important step in the laying of the 
foundations of chemistry as an exact science, and furnishes a model 
of carefully planned experimental investigation, and of clear 
reasoning upon the results of experiment. . . . Attention may be 
particularly called to Black's tacit adoption of the quantitative 
method in a large number of his experiments, and to the way in 
which he bases many of his conclusions upon the results obtained 
in these experiments. 

Joseph Black 167 

The problem that Black set out to solve was the nature 
of the changes that occur when quicklime is added to the 
'mild' alkalis (potassium and sodium carbonates) to render 
them caustic, that is, in modern terms, to convert them into 
potassium and sodium hydroxides. The caustic nature of the 
quicklime formed when chalk is strongly heated was explained 
on the phlogiston theory by assuming that the chalk had taken 
up phlogiston from the fire. Black, however, observed (i) that 
a loss in weight occurs when chalk is converted into quicklime, 
and (2) that this loss in weight is due to the fact that a g&s, fixed 
air [carbon dioxide], is evolved in the reaction. He found, more- 
over, that magnesia alba [a carbonate of magnesium] underwent 
a similar change when strongly heated, but that heat had no 
effect upon the fixed 'mild' alkalis. 

It is sufficiently clear [he says] that the calcarious earths in their 
native state, and that the alkalis and magnesia in their ordinary 
condition, contain a large quantity of fixed air, and this air cer- 
tainly adheres to them with considerable force, since a strong fire is 
necessary to separate it from magnesia, and the strongest is not 
sufficient to expel it entirely from fixed alkalis, or take away their 
power of effervescing with acids. . . . Crude lime [limestone] was 
therefore considered as a peculiar acrid earth rendered mild by its 
union with fixed air: and quicklime as the same earth, in which, by 
having separated the air, we discover that acrimony or attraction 
for water, for animal, vegetable, and for inflammable substances. 

With remarkable insight he goes on to explain the reaction 
between slaked lime and carbon dioxide : 

A calcarious earth deprived of its [fixed] air, or in the state of quick- 
lime, greedily absorbs a considerable quantity of water, becomes 
soluble in that fluid, and is then said to be slaked ; but as soon as it 
meets with fixed air, it is supposed to quit the water and join itself 
to the air, for which it has a superior attraction, and is therefore 
restored to its first state of mildness and insolubility in water. 

When slaked lime is mixed with water, the fixed air dissolved in 
the water is attracted by the lime, and saturates a small portion of 
it, which then becomes again incapable of dissolution, but part of 
the remaining slaked lime is dissolved and composes lime-water. 

1 68 Joseph Black 

If this fluid be exposed to the open air, the particles of quicklime 
which are nearest the surface gradually attract the particles of fixed 
air which float in the atmosphere. But at the same time that 
a particle of lime is thus saturated with air, it is also restored to its 
native state of mildness and insolubility; and as the whole of this 
change must happen at the surface, the whole of the lime is 
successively collected there under its original form of an insipid 
calcarious earth, called the cream or crusts of lime-water. 

Black had thus arrived at an astonishingly accurate con- 
ception of the constitution of limestone and of magnesia alba, 
and was now in a position to bring his knowledge to bear upon 
the original problem, namely, to explain the reaction that 
occurs between quicklime and the 'mild' alkalis. In the first 
place he knew that both limestone and the mild alkalis effer- 
vesced when treated with dilute acids. He reasonably supposed 
that the gas evolved in the former case was fixed air, and he 
obtained a proof of this assumption by experiments in which he 
found (a) that no gas 'is separated from quicklime by an acid, 
and that chalk saturates nearly the same quantity of an acid after 
it is converted into quicklime as before', and (b) that two drams 
of chalk lost the same weight of 'air' when treated with a dilute 
acid as when heated strongly in a furnace. 

He next showed that if a definite weight of chalk was taken 
and converted into quicklime, the latter could be reconverted 
into chalk by treatment with a solution of a mild alkali, and that 
the weight of the chalk thus formed was equal to that of the 
original specimen. The lime therefore had been 'saturated with 
fixed air which must have been furnished by the alkali'. 

On exposing a solution of caustic alkali to the air for some 
time, Black found that 'the alkali lost the whole of its causticity, 
and seemed entirely restored to the state of an ordinary fixed 
alkali', and this he explained by assuming that the caustic alkali 
had absorbed fixed air from the atmosphere. 

From this remarkable series of experiments he had thus 
obtained results that enabled him to explain satisfactorily the 
whole problem. Limestone was a compound of quicklime with 

Joseph Priestley 169 

fixed air; when heated it lost the fixed air, quicklime being left. 
The mild alkalis were compounds of fixed air with substances 
resembling quicklime, but much more soluble in water. When 
a solution of a mild alkali was treated with quicklime, the latter 
absorbed the fixed air of the former, with production of insoluble 
chalk or limestone ; the filtrate was therefore a solution of caustic 
alkali. In all essentials, Black's explanation is identical with our 
own, and the careful logic of his procedure makes his mono- 
graph conspicuous at once among the multitudes of useful re- 
searches that were now beginning to bear witness to the new 
spirit in chemistry. His only other important discovery was that 
of the bicarbonates, but he is nevertheless correctly regarded as 
one of the greatest chemists of one of the most fruitful periods of 
chemistry, and his fame rests upon impregnable foundations. 

42. Joseph Priestley 

THE phlogiston theory of combustion found its most ardent 
supporter in the person of Joseph Priestley, who was born about 
six miles from Leeds, in 1733, and at the age of twenty-two 
became a Unitarian pastor. To supplement his meagre income 
he undertook teaching work in addition, and showed such ability 
that in 1761 he was appointed to the chair of languages and 
literature at the Warrington Academy. Further promotion 
came in 1767, when he became pastor of a large congregation in 
Leeds. Six years later his reputation as a scientist and philo- 
sopher was thoroughly established, and he accepted an invita- 
tion from Lord Shelburne (the first Marquis of Lansdowne) to 
fill the post of his lordship's companion and librarian at Bowood 
(Wiltshire). Here he had ample time for the scientific researches 
that were his principal delight, and the eight years during 
which the association lasted were among the most fruitful of his 
life. In 1780 he was elected junior minister of the New Meeting, 
Birmingham, and resigned his post with Lord Shelburne, who, 
however, presented him with an annuity of 150. 

During the unsettled period of the French Revolution, 
Priestley openly expressed sympathy with the revolutionaries, 

1 70 Joseph Priestley 

and was indeed one of their warmest advocates in this country. 
He particularly provoked the great Burke by his reply to the 
latter's book on the Revolution, and also drew upon himself the 
animosity of the orthodox clergy by his attacks on the Estab- 
lished Church. The feeling of the country was roused against 

#'tg. 54. JUbJt^rt 

him, and on 14 July 1791, the anniversary of the fall of the 
Bastille, the Birmingham mob wrecked his house and made 
a bonfire of his furniture and books. He himself made a hurried 
escape to London, travelling on the stage-coach under an 
assumed name. Matters were not mended by the action of the 
French Assembly which, in September 1792, made him a 
citizen of France, and finally he thought it wise to emigrate to 
America, whither his three sons had preceded him. He set sail 
for New York in April 1794, and was well received in scientific 
and religious circles; but he refused to become a naturalized 

Joseph Priestley 171 

American and also declined the offer of the professorship of 
chemistry at Philadelphia. After a short time he established 
himself in Pennsylvania, and spent the remaining years of his 
life in honoured retirement. He died in 1804. 

Passionately devoted to the study of gases, the 'father of 


pneumatic chemistry' seems to have had no definite working 
plan but to have strayed whither his fancy took him. This 
fortunate trait was directly responsible for his most celebrated 
discovery, for on i August 1774 it led him to investigate the 
effect of heat upon the red calx of mercury. A moment's 
reflection will show us that had Priestley, as a staunch phlogis- 
tian, stopped to consider the experiment he was about to per- 
form, he would probably have changed his mind. "This calx', 
he would have said, 'is only mercury from which the phlogiston 
has been removed. Now it is just this removal of phlogiston 
that is the characteristic effect of heat upon a metal, a mere 

172 Joseph Priestley 

calx being left. Why waste time in heating a substance upon 
which heat has already performed its action?' 

However, one's mental activities are not as a rule at their best 
on a warm Sunday afternoon in summer, and, moreover, 
Priestley had just become the happy possessor of a fine new 
burning-glass or convex lens. Tradition says that this lens had 
formerly belonged to the Grand-Duke Cosmo III of Tuscany, 
who had amused himself by burning his subjects' diamonds 
with it. Whether this is true or not we need not stay to inquire : 
it is sufficient to know that Priestley was highly delighted with 
his splendid new instrument, and 'proceeded with great alacrity 
to examine, by the help of it, what kind of air a great variety 
of substances, natural and factitious [artificial], would yield, put- 
ting them into . . . vessels . . . which I filled with quicksilver, and 
kept inverted in a bason of the same'. Among the substances 
chosen was the red calx of mercury, a choice which, as we have 
seen, was merely a fortunate accident. Priestley himself, on 
looking back, frankly remarks that it was a matter of chance : 
The contents of this section will furnish a very striking illustration 
of the truth of a remark, which I have more than once made in my 
philosophical writings, and which can hardly be too often repeated, 
as it tends greatly to encourage philosophical investigations; viz. 
that more is owing to what we call chance, that is, philosophically 
speaking, to the observation of events arising from unknown causes, 
than to any proper design, or preconceived theory in this business. 
. . . For my own part, I will frankly acknowledge, that, at the com- 
mencement of the experiments recited in this section, I was so far 
from having formed any hypothesis that led to the discoveries I made 
in pursuing them, that they would have appeared very improbable 
to me had I been told of them ; and when the decisive facts did at 
length obtrude themselves upon my notice, it was very slowly, and 
with great hesitation, that I yielded to the evidence of my senses. 

When the mercury calx was heated, Priestley saw with amaze- 
ment that mercury was formed and that a colourless 'air' was 
expelled. 'But what surprised me more than I can well express, 
was that a candle burned in this air with a remarkably brilliant 
flame.' In general properties the gas resembled ordinary air, 

Joseph Priestley 173 

but it would support combustion very much better, and a mouse 
was able to live in it for nearly twice as long as it could have lived 
in the same volume of air. We may well sympathize with 
Priestley's surprise. No result could have been more unexpected, 


and Priestley's difficulty in explaining it can be imagined. It 
did not occur to him that the phlogiston theory was inadequate 
to account for these new and astonishing phenomena; the 
problem as he saw it was to reconcile the theory with the observa- 
tions he had made. This he proceeded to do, unmindful of the 
warning he had himself expressed: 

We may take a maxim so strongly for granted that the plainest 
evidence of sense will not entirely change, and often hardly modify, 
our persuasions; and the more ingenious a man is, the more 
effectually he is entangled in his errors, his ingenuity only helping 
him to deceive himself by evading the force of truth. 

^ l^^ f~*'f -*~* J^*^ /"//*-* <~y;. 

*4? >+^6(*? 

4u~ " 

&~s j~- 

. ^, 


Priestley obviously experienced the utmost difficulty in 
arriving at a clear conclusion on the nature of the changes he 
had observed. His train of thought is confused and inconsistent, 
but two points at length emerge distinctly. They are (a) that 
ordinary air must contain phlogiston, and (b) that his new gas 
represented air which had been deprived of its phlogiston ; he 
therefore called it dephlogisticated air. As to point (a), it is plain 
that since phlogiston is considered to be evolved from all burn- 
ing substances, the air must contain a good deal of it. Moreover, 
Priestley had shown the close connexion that exists between 
combustion and respiration, and in the latter process there was 
clearly a second source of atmospheric phlogiston. On respira- 
tion and putrefaction he remarks that they 'affect common air 
in the same manner in which all noxious processes diminish air 
and make it noxious and which agree in nothing but the emission 
of phlogiston. If this be the case it should seem that the phlogis- 
ton which we take in with our aliment, after having discharged 
its proper function in the animal system, is discharged as 
effete by the lungs into the great common menstruum, the 

There was, then, no difficulty in assuming that the atmo- 
sphere, in its normal condition, is charged with a certain pro- 
portion of phlogiston. Now the capability of air of supporting 

176 Joseph Priestley 

combustion was considered to be a function of its power of 
absorbing phlogiston. Air, therefore, deprived of its phlogiston 
can naturally absorb more than could the same volume of 
ordinary air; dephlogisticated air is air of this kind and its 
properties are thus explained. Such, in short, was Priestley's 
reasoning, and it fitted the facts moderately well. 

But there was still the difficulty of explaining why mercury 
calx, which presumably is simply the earthy residue of mercury, 
should be able to yield dephlogisticated air when heated, and it 
is here that Priestley floundered in a morass of involved hypo- 
theses. To trace his steps closely lies outside the province of 
this book, but he seems to have argued as follows. When 
mercury is calcined, it is true that its phlogiston is liberated 
from combination with the calx, but instead of going off into the 
air it absorbs pure air, i.e. air minus phlogiston, or dephlogisti- 
cated air, and the phlogisticated air thus produced remains fixed 
in a mechanical way in the particles of calx. Upon heating the 
calx, the phlogisticated air is split up, its phlogiston combining 
with the calx to re-form metallic mercury while its dephlogisti- 
cated air is evolved. It is, however, impossible to give a definite 
account of Priestley's views, since they were themselves never 
clearly outlined : his own statement may be reproduced in order 
to give the reader an opportunity of arriving at an independent 
interpretation : 

The phlogiston belonging to the metal unites with that air [pure 
or dephlogisticated air] so as together to form fixed air [which is not, 
in this case, carbon dioxide as with Black], and therefore the calx 
may be said to be the metal united to fixed air. Then, in a greater 
degree of heat than that in which the union was formed, this 
factitious fixed air is again decomposed; the phlogiston in it 
reviving the metal, while the pure air is set loose. Consequently 
the precipitate mercury calx actually contains within itself all the 
phlogiston that is necessary to the revival of the mercury. 

In October 1774 Priestley accompanied Lord Shelburne to 
Paris. Here he was invited to dine with the French chemist 
Lavoisier, and the meeting, which was fraught with tremendous 

Henry Cavendish 177 

consequences for chemistry, may be described in Priestley's own 
words : 'Having made the discovery of dephlogisticated air some 
time before I was in Paris, in the year 1774, 1 mentioned it at the 
table of Mr. Lavoisier, when most of the philosophical people of 
the city were present, saying that it was a kind of air in which 
a candle burnt much better than in common air, but I had not 
then given it any name. At this all the company, and Mr. and 
Mrs. Lavoisier as much as any, expressed great surprise. I told 
them I had gotten it horn precipitate per se [calx of mercury] and 
also from red lead. Speaking French very imperfectly, and being 
little acquainted with the terms of chemistry, I saidplombe rouge, 
which was not understood till Mr. Macquer said I must mean 
minium. 9 

In a short time we shall see the results of this historic meeting, 
but in the meanwhile we must leave Priestley in order to form 
the acquaintance of 'the richest of the learned and the most 
learned of the rich', the Hon. Henry Cavendish. 

43. Henry Cavendish 

CAVENDISH was a member of the family of the Duke of Devon- 
shire, and was born at Nice in 1731. His appearance Mid not 
much prepossess strangers in his favour; he was somewhat 
above the middle size, his body rather thick, and his neck rather 
short. He stuttered a little in his speech, which gave him an air 
of awkwardness : his countenance was not strongly marked, so 
as to indicate the profound abilities which he possessed'. Of 
a quiet and retiring disposition, he shunned publicity of all kinds, 
and carried out his experiments solely for his own satisfaction. 
Caring little for worldly pleasures, he made but small inroads 
into his money, although he provided a library for the use of the 
scientific public and was even generous enough to give ^10,000 
to one of the temporary librarians who fell ill. 

'He was shy and bashful to a degree bordering on disease; he 
could not bear to have any person introduced to him, or to be 
pointed out in any way as a remarkable man. One Sunday 
evening he was standing at Sir Joseph Banks 's in a crowded 

178 Henry Cavendish 

room, conversing with Mr. Hatchett, when Dr. Ingenhousz, 
who had a good deal of pomposity of manner, came up with an 
Austrian gentleman in his hand, and introduced him formally 
to Mr. Cavendish. He mentioned the titles and qualifications of 

his friend at great length, 
and said that he had been 
peculiarly anxious to be in- 
troduced to a philosopher so 
profound and so universally 
known and celebrated as 
Mr. Cavendish. As soon as 
the Austrian gentleman be- 
gan , and assured Mr. Caven- 
dish that his principal rea- 
son for coming to London 
was to see and converse with 
one of the greatest orna- 
ments of the age, and one 
of the most illustrious philo- 
sophers that ever existed. 
To all these high-flown 
speeches Mr. Cavendish 
answered not a word, but 
stood with his eyes cast 
down quite abashed and 
confounded . At last , spying 
an opening in the crowd, he 
darted through it with all 
the speed of which he was master; nor did he stop till he 
reached his carriage, which drove him directly home.' 

Cavendish's chief contributions to chemistry were his work on 
gases and his discovery of the composition of water and of nitric 
acid. In 1766 he published in the Philosophical Transactions of 
the Royal Society three papers, entitled 'Experiments on 
Factitious Air'. In these he described the preparation of an 

r/X /) / 

\s* L "fl f 

18 ' 

Henry Cavendish 179 

inflammable air [hydrogen] by the action of dilute sulphuric or 
hydrochloric acid upon zinc, iron, or tin. 

Zinc [he says] dissolves with great rapidity in both these acids; 

and, unless they are very much diluted, generates considerable 

heat. One ounce of zinc produces about 356 

ounce measures of air: the quantity seems just 

the same whichever of these acids it is dissolved 

in. Iron dissolves readily in the diluted vitriolic 

[sulphuric] acid, but not near so readily as zinc. 

One ounce of iron wire produces about 412 

ounce measures of air: the quantity was just the 

same, whether the oil of vitriol was diluted with 

i^, or 7 times its weight of water: so that the 

quantity of air seems not at all to depend on the 

strength of the acid. I know of only three 

metallic substances, namely, zinc, iron, and tin, 

that generate inflammable air by solution in 

acids; and those only by solution in the diluted 

vitriolic acid, or spirit of salt. 

He determined the density of the gas (al- 
though the value he obtained was very in- 
accurate), and discovered its chief chemical 
properties, from a study of which he concluded 
that the gas was practically pure phlogiston and 
was derived from the metals, not from the acids. 
The action of nitric acid on metals was found 
to yield an incombustible air, generally nitric 
oxide, a result that he explained by assuming 
that the phlogiston had reacted with the acid. 

Cavendish also conducted experiments on 
Black's 'fixed air' [carbon dioxide], measuring 
its density and determining its solubility in water. In this 
connexion it is interesting to note that Cavendish, making use 
of an observation of Boerhaave's, was the first to introduce a 
method of drying a gas, which he did by passing it through dry 
potassium carbonate or pearl-ashes. He also invented the 
method of storing gases over mercury, an idea that inspired 

N 2 

Fig- 59- 


180 Henry Cavendish 

Priestley to use mercury instead of water in the pneumatic 
trough. It is, however, for his work on the composition of water 
and of nitric acid that he is chiefly remembered, and to an 
account of these experiments we must now proceed. 

In 1781, Priestley and his friend Warltire had both noticed 
that on firing a mixture of common and inflammable airs in a 
clean and dry glass vessel, by means of an electric spark, 'the 
inside of the glass . . . immediately became dewy'. This experi- 
ment was repeated by Cavendish, who published his results in 
the Philosophical Transactions of the year 1784. He found that 
In all the experiments the inside of the glass globe became dewy, 
as observed by Mr. Warltire ; but not the least sooty matter could 
be perceived. Care was taken in all of them to find how much the 
air was diminished by the explosion. . . . The result is as follows: 
the bulk of the inflammable air being expressed in decimals of the 
common air. 

Inflammable Air remaining 

Common Air. Air. Diminution. after the Explosion. 

1-241 0686 i'555 

i 055 o 642 1-413 

o 706 o 647 1-059 

0-423 o 612 o 811 

0-331 0476 0855 

0-206 o 294 0-912 

. . . From the fourth experiment it appears, that 423 measures of 
inflammable air are nearly sufficient to completely phlogisticate 
1,000 of common air; and that the bulk of the air remaining after 
the explosion is then very little more than four-fifths of the common 
air employed ; so that as common air cannot be reduced to a much 
less bulk than that by any method of phlogistication, we may safely 
conclude, that when they are mixed in this proportion, and ex- 
ploded, almost all the inflammable air, and about one-fifth part of 
the common air, lose their elasticity, and are condensed into the 
dew which lines the glass. 

The better to examine the nature of this dew, 500,000 grain 
measures of inflammable air were burnt with about 2\ times that 
quantity of common air, and the burnt air made to pass through 
a glass cylinder eight feet long and three-quarters of an inch in 
diameter, in order to deposit the dew. The two airs were con- 

Henry Cavendish 181 

veyed slowly into this cylinder by separate copper pipes, passing 
through a brass plate which stopped up the end of the cylinder; 
and as neither inflammable nor common air can burn by themselves, 
there was no danger of the flame spreading into the magazines 
from which they were conveyed. Each of these magazines con- 
sisted of a large tin vessel, inverted into another vessel just big 
enough to receive it. The inner vessel communicated with the 
copper pipe, and the air was forced out of it by pouring water into 
the outer vessel ; and in order that the quantity of common air 
expelled should be 2\ times that of the inflammable, the water was 
let into the outer vessel by two holes in the bottom of the same tin 
pan, the hole which conveyed the water into that vessel in which the 
common air was confined being 2\ times as big as the other. 

In trying the experiment, the magazines being first filled with 
their respective airs, the glass cylinder was taken off, and water let, 
by the two holes, into the outer vessels, till the airs began to issue 
from the ends of the copper pipes ; they were then set on fire by 
a candle, and the cylinder put on again in its place. By this means 
upwards of 135 grains of water were condensed in the cylinder, 
which had no taste nor smell, and which left no sensible sediment 
when evaporated to dryness ; neither did it yield any pungent smell 
during the evaporation ; in short, it seemed pure water. 

In my first experiment, the cylinder near that part where the air 
was fixed was a little tinged with sooty matter, but very slightly so ; 
and that little seemed to proceed from the putty with which the 
apparatus was luted, and which was heated by the flame; for in 
another experiment, in which it was contrived so that the luting 
should not be much heated, scarce any sooty tinge could be 

By the experiments with the globe it appeared, that when in- 
flammable and common air are exploded in a proper proportion, 
almost all the inflammable air, and near one-fifth of the common 
air, lose their elasticity, and are condensed into dew. And by this 
experiment it appears, that this dew is plain water, and con- 
sequently that almost all the inflammable air, and about one-fifth 
of the common air, are turned into pure water. 

Cavendish had thus shown that water, instead of being an 
element, was a compound of inflammable air [hydrogen] with 

1 82 Henry Cavendish 

a part of common or atmospheric air a part which appeared to 
form one-fifth of the whole. Knowing of the astonishing power 
of supporting combustion possessed by Priestley's dephlogisti- 
cated air, Cavendish was anxious to find out what happened 
when inflammable air and dephlogisticated air were exploded 


together, and carried out experiments with this aim immediately 
after those just described. He says: 

In order to examine the nature of the matter condensed on firing 
a mixture of dephlogisticated and inflammable air, I took a glass 
globe, holding 8,800 grain measures, furnished with a brass cock 
and an apparatus for firing air by electricity. This globe was well 
exhausted by an air-pump, and then filled with a mixture of in- 
flammable and dephlogisticated air, by shutting the cock, fastening 
a bent glass tube to its mouth, and letting up the end of it into 
a glass jar inverted into water, and containing a mixture of 19,500 
grain measures of dephlogisticated air, and 37,000 of inflammable ; 
so that, upon opening the cock, some of this mixed air rushed 
through the bent tube, and filled the globe. (In order to prevent 
any water from getting into this tube, while dipped under water to 
let it up into the glass jar, a bit of wax was stuck upon the end of it, 
which was rubbed off when raised above the surface of the water.) 
The cock was then shut, and the included air fired by electricity, 
by which means almost all of it lost its elasticity. The cock was 
then again opened, so as to let in more of the same air, to supply 

Henry Cavendish 183 

the place of that destroyed by the explosion, which was again fired, 
and the operation continued till almost the whole of the mixture 
was let into the globe and exploded. By this means, though the globe 
held not more than the sixth part of the mixture, almost the whole 
of it was exploded therein, without any fresh exhaustion of the globe. 



As a result of this experiment, Cavendish obtained about 
thirty grains of water, and concluded 'that dephlogisticated air 
is in reality nothing but dephlogisticated water, or water de- 
prived of its phlogiston; or, in other words, that water consists 
of dephlogisticated air united to phlogiston ; and that inflam- 
mable air is either pure phlogiston, as Dr. Priestley and Mr. 
Kirwan suppose, or else water united to phlogiston'. The 
Richard Kirwan (1733-1812) here referred to was an Irish savant 
who had settled down in London, devoting himself to experi- 
mental chemistry. 

Cavendish had thus accurately determined the composition of 
water, and had shown that it was quite definitely not an element, 
thus driving the last nail into the coffin of Aristotelian chemical 
theory, and affording more valuable material for elaboration by 
Lavoisier. Cavendish mentions that a friend of his gave an 
account of the foregoing experiments to 'M. Lavoisier, as well as 
of the conclusion drawn from them, that dephlogisticated air is 
only water deprived of phlogiston ; but at that time so far was 
M. Lavoisier from thinking any such opinion warranted, that, 

184 Henry Cavendish 

till he was prevailed upon to repeat the experiment himself, he 
found some difficulty in believing that nearly the whole of the 
two airs could be converted into water'. 

The glass globe in which Cavendish's historic experiment was 
made may (Fig. 59) still be seen in a case in one of the corridors of 
the Chemistry Department of the University of Manchester ; there 
seems little doubt of the authenticity of the exhibit, as Professor 
Partington tells us that its pedigree can be traced fairly com- 

Cavendish's investigation of the composition of nitric acid was 
of almost equal importance with his researches on water. Nitric 
acid has been known for centuries, and its preparation by heating 
a mixture of alum, vitriol, and saltpetre is described by Jabir 
(see p. 60). It was known also to other Arab chemists, who used 
it for separating the silver from the gold in a gold-silver alloy. 
Glauber (1604-68) prepared it by heating a mixture of saltpetre 
and sulphuric acid, and by the middle of the eighteenth century 
it was obtainable in quantity from the chemical manufacturers. 
In 1784 Cavendish conducted a series of experiments on the 
effect of sparking a mixture of moist dephlogisticated air 
[oxygen] and phlogisticated air [nitrogen]. The apparatus he 
employed is shown in Fig. 61. 

The air through which the spark was intended to be passed [he says] 
was confined in a glass tube Af, bent to an angle (p. 183), which, 
after being filled with quicksilver, was inverted into two glasses of 
the same fluid, as in the figure. The air to be tried was then intro- 
duced by means of a small tube, such as is used for thermometers, 
bent in the manner represented by ABC (Fig. 61), the bent end of 
which, after being previously filled with quicksilver, was intro- 
duced, as in the figure, under the glass DBF, inverted into water, 
and filled with the proper kind of air, the end C of the tube being 
kept stopped by the finger; then, on removing the finger from C, 
the quicksilver in the tube descended in the leg BC, and its place 
was supplied with air from the glass DEF. Having thus got the 
proper quantity of air into the tube ABC, it was held with the end 
C uppermost, and stopped with the finger; and the end A y made 
smaller for that purpose, being introduced into one end of the 

Henry Cavendish 185 

bent tube M (Fig. 61), the air, on removing the finger from C, was 
forced into that tube by the pressure of the quicksilver in the leg 
BC. By these means I was enabled to introduce the exact quantity 
I pleased of any kind of air into the tube M ; and, by the same 
means, I could let up any quantity of soap-lees, or any other 
liquor which I wanted to be in contact with the air. . . . 

I now proceed to the experiments. When the electric spark was 
made to pass through common air, included between short 
columns of a solution of litmus, the solution acquired a red colour, 
and the air was diminished, conformably to what was observed by 
Dr. Priestley. . . . When the air is confined by soap-lees, the 
diminution proceeds rather faster than when it is confined by 

It must be considered, that common air consists of one part of 
dephlogisticated air, mixed with four of phlogisticated ; so that 
a mixture of five parts of pure dephlogisticated air, and three of 
common air, is the same thing as a mixture of seven parts of 
dephlogisticated air with three of phlogisticated. 

I introduced into the tube a little soap-lees, and then let up 
some dephlogisticated and common air, mixed in the above- 
mentioned proportions, which rising to the top of the tube M, 
divided the soap-lees into its two legs. As fast as the air was 
diminished by the electric spark, I continued adding more of the 
same kind, till no further diminution took place : after which a little 
pure dephlogisticated air, and after that a little common air, were 
added, in order to see whether the cessation of diminution was not 
owing to some imperfection in the proportion of the two kinds of 
air to each other; but without effect. The soap-lees being then 
poured out of the tube, and separated from the quicksilver, 
seemed to be perfectly neutralized, as they did not at all discolour 
paper tinged with the juice of blue flowers. Being evaporated to 
dryness, they left a small quantity of salt, which was evidently 
nitre, as appeared by the manner in which paper, impregnated 
with a solution of it, burned. 

From these experiments it was clear that 'phlogisticated air' 
is a constituent of nitre and of nitric acid, and the first stage in 
the elucidation of the constitution of the acid had therefore been 
established. It was left to later chemists to complete the solution 

1 86 Karl Wilhelm Scheele 

of the problem, notably the brilliant French scientist Gay- 

In the course of the experiments that have just been de- 
scribed, Cavendish made an observation of much interest an 
observation, however, the importance of which was not appre- 
ciated until over a century later. In 1784 he 'diminished a mix- 
ture of dephlogisticated and common air [by means of the 
electric spark] in the same manner as before, till it was reduced 
to a small part of its original bulk'. Then, he says: 

In order to decompound as much as I could of the phlogisticated 
air which remained in the tube, I added some dephlogisticated air 
to it, and continued the spark till no further diminution took place. 
Having by these means condensed as much as I could of the 
phlogisticated air, I let up some solution of liver of sulphur to 
absorb the dephlogisticated air ; after which only a small bubble of 
air remained unabsorbed, which certainly was not more than -^ 
of the bulk of the phlogisticated air let up into the tube ; so that if 
there is any part of the phlogisticated air of our atmosphere which 
differs from the rest, and cannot be reduced to nitrous acid, i.e. 
converted into nitric acid, we may safely conclude that it is not 
more than j| 5 part of the whole. 

In 1895 Lord Rayleigh and Professor (later Sir) William 
Ramsay showed that this bubble of intractable gas contained an 
extremely unreactive element, to which they gave the name of 
argon, and a short time afterwards the presence of other in- 
active gases mixed with the argon was demonstrated. No more 
striking testimony to the skill and accuracy of Cavendish's 
work could be desired. 

44. Karl Wilhelm Scheele 

PRIESTLEY and Cavendish, brilliant experimenters as they were, 
fell short in this respect of a poor Swedish apothecary named 
Karl Wilhelm Scheele. Scheele was one of those men who have 
an instinctive flair for experimental work every teacher of 
chemistry must have experienced the phenomenon among his 
pupils but Scheele possessed the instinct in a superlative 

Karl Wilhelm Scheele 187 

degree. It is not necessarily accompanied by a capacity for pro- 
found scientific thought ; on the contrary, the brilliant experi- 
menter and investigator is often but a mediocre thinker, as 
witness Priestley and Lemery. Scheele himself was no theorist 
and accepted the phlogiston system unquestioningly, but as 
a discoverer of chemical facts he has few, if any, equals. 

Scheele was born at Stralsund, in Swedish Pomerania, on 
19 December 1742. At 14 years of age he was apprenticed to 
Bauch, an apothecary of Gothenburg, with whom he remained 
for eight years. In 1765 he went to Malmo, in 1767 to Stock- 
holm, and in 1773 to Upsala, in each town holding a post as an 
apothecary 's assistant and in his spare time throwing himself 
enthusiastically into researches on experimental chemistry. In 
1775 he was placed in charge of an apothecary's shop at Koping, 
on Lake Maelar, to run the business on behalf of the deceased 
proprietor's widow. Two years later he bought the shop, and in 
1786 married his predecessor's widow, only to die within forty- 
eight hours. 

Brief as his life was, he found time to make a series of dis- 
coveries of incalculable importance. Sir Edward Thorpe, in his 
excellent little History of Chemistry (London, 1909), summarizes 
them as follows : 

Scheele 'first isolated chlorine, and determined the in- 
dividuality of manganese and baryta. He was an independent 
discoverer of oxygen, ammonia, and hydrogen chloride. He 
discovered also hydrofluoric, nitro-sulphonic,molybdic,tungstic 
and arsenic, among the inorganic acids ; and lactic, gallic, pyro- 
gallic, oxalic, citric, tartaric, malic, mucic and uric acids among 
the organic acids. He isolated glycerine and milk-sugar; deter- 
mined the nature of microcosmic salt, borax, and Prussian blue, 
and prepared hydrocyanic [prussic] acid. He demonstrated that 
graphite is a form of carbon. He discovered the chemical nature 
of sulphuretted hydrogen, arseniuretted hydrogen, and the green 
arsenical pigment known by his name. He invented new pro- 
cesses for preparing ether, powder of algaroth, phosphorus, 
calomel, and magnesia alba. He first prepared ferrous ammonium 

1 88 Karl Wilhelm Scheele 

sulphate ; showed how iron may be analytically separated from 
manganese ; and described the method of breaking up mineral 
silicates by fusion with alkaline carbonates'. Can a like array of 
discoveries be claimed by any other chemist except, perhaps, 
Emil Fischer? 

A year or more before Priestley performed his celebrated 
experiment on calx of mercury, Scheele had obtained a gas which 
he called Feuerluft or fire-air by the action of heat upon (a) a 
mixture of saltpetre and oil of vitriol, (b) red calx of mercury, 
(r) saltpetre alone, (d) pyrolusite [manganese dioxide], and other 
substances. This, of course, is identical with dephlogisticated 
air, but Scheele 's publishers were slow, and his results were not 
made public until 1777, so t ^ at priority in the discovery is 
usually assigned to Priestley. Scheele, however, definitely con- 
cluded that ordinary air consists of 'two kinds of elastic fluid' or 
gas, noticed that part of the air was lost in combustion, and 
observed that the residual air was relatively lighter than the 
original air. The part of the air which was lost during com- 
bustion he was unable to find again. He remarks that it might be 
suggested that 'the lost air still remains in the residual air which 
can no more unite with phlogiston ; for, since I have found that 
it is lighter than ordinary air, it might be believed that the 
phlogiston united with this air makes it lighter, as appears to be 
known already from other experiments. But since phlogiston is 
a substance, which always presupposes some weight, I much 
doubt whether such hypothesis has any foundation'. How near 
Scheele was to a supreme discovery ! 

During the course of an investigation of pyrolusite, a black 
mineral found in Spain, Asia Minor and certain other localities, 
Scheele heated the substance with spirit of salt or marine acid 
[hydrochloric acid] and observed the formation of a greenish- 
yellow gas [chlorine]. He explained the reaction by assuming 
that the pyrolusite had dephlogisticated the marine acid, i.e. 
removed phlogiston from it, and therefore called the new gas 
dephlogisticated marine acid. He noticed that the gas attacked 
organic matter, that it would bleach litmus and coloured flowers, 

Guillaume Francois Rouelle 189 

that its solution on standing became converted into a solution of 
marine acid, that it attacked metals, that it formed a white cloud 
with ammonia, that it was poisonous, and that it would not 
support ordinary combustion. The proof of the elementary 
nature of Scheele's 'dephlogisticated marine acid', and its later 
name chlorine, are both due to Sir Humphry Davy (p. 260). 

Scheele's devotion to chemistry cost him his life, for it was 
doubtless exposure to cold in the unheated shop and the inhalation 
of fumes from his experiments, not to mention the enormous 
demands he made upon his physical strength in managing 
a business as well as performing ceaseless research, that caused 
the breakdown in his health and brought him to an early grave. 
He refused honours that were offered him, preferring, like van 
Ilelmont, to remain in peaceful obscurity. 'Avec cle petites 
ressources, il fit de grandes choses', says a chronicler, and it 
would be difficult to find more appropriate words. 

45. Guillaume Franfois Rouelle 

THE eccentric personality of Cavendish finds its counterpart 
across the Channel in Guillaume Franois Rouelle, one of the 
greatest teachers of chemistry that France, or indeed the world, 
has ever produced. Rouelle was born in 1703, at the village of 
Mathieu, in Normandy, and after preliminary education at the 
College of Caen he went to Paris. Here he studied chemistry 
and pharmacy with such success that, about the middle of the 
century (1742), he was appointed Demonstrator of chemistry at 
the Jardin du Rot. The courses in chemistry at the Jardin were 
open to the public, and were conducted concurrently by a pro- 
fessor of theory and a demonstrator of practice. The arrange- 
ment is humorously described by Hoefer, the historian of 
chemistry, whose books are written in a delightful style that 
hides the wide scholarship beneath : 

The interminable contention [says Hoefer] between theory and 
practice was later personified by the Professor and the Demon- 
strator, charged, under Louis XIV and Louis XV, with the teach- 
ing of chemistry at the Jardin du Roi. The Professor, soaring in 

190 Guillaume Frai^ois Rouelle 

the realms of abstract principle, regarded it beneath his dignity to 
descend to the details of the laboratory and to soil his fingers with 
charcoal dust. He, indeed, was Theory: a role which was filled by 
the First Physician of the King. After the Professor had finished 
lecturing the Demonstrator arrived. His duty was to support the 
speculative views of the Professor by experimental facts : he was , 
in fact, Practice. 

It was Rouelle (1703-70) who, under Louis XV, fulfilled the 
functions of Demonstrator at the Jar din du Roi\ Bourdelain 
occupied the chair of chemistry there. The Professor, who was 
received coldly, invariably finished his lecture with the words 
1 Such, gentlemen, are the principles and the theory of this opera- 
tion, as the Demonstrator is about to prove to you by his experi- 
ments/ Rouelle made his appearance immediately afterwards 
amidst the plaudits of the audience, but, nearly always, M. le 
Demonstrates upset, by his experiments, the theories of M. le 

Rouelle was a very original man; he had in him something of 
Paracelsus and Bernard Palissy. He used to come into the lecture- 
room elegantly attired : velvet coat, powdered wig, and a little hat 
under his arm. Collected enough at the beginning of his lecture, 
he gradually became more animated. If his train of thought became 
obscure, he lost patience; he would put his hat on a retort, take off 
his wig and untie his cravat. Then, talking all the while, he would 
unbutton his coat and waistcoat and take them off one after the other. 

Rouelle was helped in his experiments by one of his nephews, 
but as tfeis help was not always to be found close at hand he used 
to call with an ear-splitting shout, 'Nephew! O that eternal 
nephew!' and the eternal nephew not appearing he would himself 
depart into the back regions of his laboratory to find the object he 
needed. Meanwhile he used to continue his lecture as though he 
were still in the presence of his audience. When he returned he 
had generally finished the demonstration which he had begun, and 
would come in again saying, ' There, gentlemen, that is what I had 
to tell you'. Then he was begged to begin again, which he always 
did with the best grace in the world, in the conviction that he had 
merely been badly understood. 

In his habitual absent-mindedness, Rouelle would often de- 
scribe processes that he wished to keep secret. In the warmth 

Guillaume Francois Rouelle 191 

of his discourse he would say, "This is one of my secrets which 
I will never tell any one', having just revealed it to everybody! 
Grimm relates that one day, when Rouelle was in a mixed 
company and talking with his usual vivacity, he untied his 
garter, pulled down his stocking, scratched his leg with both 


hands, replaced his stocking and garter, and continued his con- 
versation quite unconscious of what he had been doing. His 
favourite term for his opponents, or for any one of whom he dis- 
approved, was plagiarist. At the Jar din du Roi on one occasion 
the conversation turned on a recent defeat of the French army ; 
Rouelle called the French commander, the Prince de Soubise, 
a fool, a criminal and a plagiarist. 'But', said Buffon, 'it isn't 
a plagiarism to get beaten by the Prussians ; on the contrary it is 
an entirely new invention of M. de Soubise!' 'Don't defend 
him', said Rouelle, 'he 's a low animal, a horned mule, a one- 

192 Guillaume Francois Rouelle 

eyed pig! I am sure there is something vicious in his con- 

In spite of these peculiarities, Rouelle was much esteemed as 
a man and honoured as a great chemist. In 1750 he was made 
a member of the Royal Academy of Stockholm and also of that 


of Emfurt. Two years later he was elected an associate of the 
Academy of Sciences at Paris. Unfortunately, his health began 
to give way, and in 1768 he resigned his post at thejardin. For 
some months he lingered on at his house at Passy, but death 
claimed him on 3 August 1770. 

Although, like Black, Rouelle published few researches, these 
are of great importance. Yet Rouelle's chief service to chemistry 
lay in his public lectures, which were followed with eagerness 
and enthusiasm by a vast number of students, among them the 
great Lavoisier. The lectures were carefully taken down by the 
pupils, and some of their copies are still in existence: the 
Bibliotheque nationals has several examples and there is a very 
good one in the Science Library at Clifton College. The last is 
of special interest since it was transcribed from a copy belonging 
to d'Arcet, Rouelle's son-in-law, and is therefore probably very 
accurate. Its original owner, however, bitterly complains that 




O^Vt / /Y ? 

f '* 


f-7 * 





194 Guillaume Franois Rouelle 

though he paid his scribe 'cinq Louis d'or', numerous mistakes 
were made, 'que j'ai toutes corrigees de ma main de sorte que ce 
manuscrit peut passer pour tres exact et tres sur et fait un 
ouvrage tres precieux'. From the manuscript, we can gather 
that Rouelle J s course was divided into four sections. The first 
section was introductory, and gave an account of the nature, 
history, uses and principles of chemistry, from the point of view 
of a follower, but a critical follower, of Stahl. The second 
section consisted of lectures on plant life, essential oils, fixed 
alkalis, fermentation, &c., illustrated by some fifty-six experi- 
ments describing in detail the decomposition of vegetable sub- 
stances by careful distillation, extraction with solvents, and so on. 

A brief treatment of animal substances, with ten experiments, 
followed in section three. It is clear from the manuscript that 
animal chemistry offered great difficulties, and the writer says, 
'The connexion between the various phenomena presented by 
the animal kingdom has not been discovered or developed by 
any one, and is still the object of M. Rouelle 's researches'. 

The main portion of the course dealt with the mineral kingdom. 
Here Rouelle gave a full account of the chemistry of the acids, 
salts, metals and semi-metals then known, performing no fewer 
than 159 experiments in demonstration of the facts he described. 
Long dissertations on geology, alchemy and mineralogy were 
interspersed at appropriate intervals, and the course as a whole 
affords striking evidence of the versatility and originality of *le 
chef d'une ecole dont le souvenir honora son siecle et sa patrie'. 

Rouelle was the first to define clearly the nature of a salt and 
to give a systematic classification of this important class of com- 
pounds. Previous chemists had been unable to settle upon any 
definite conception of a salt, but Rouelle, with characteristic 
insight, saw directly to the heart of the problem. 'Most 
chemists', he says, 'give the name neutral, middle or "salty" salt 
to only a small number of salts ; there are even some who have 
given it to vitriolated tartar [normal potassium sulphate] alone, 
requiring as the characteristic of these salts that the acid and 
alkali which form them should be so firmly united as to resist all 

Guillaume Francis Rouelle 195 

attempts at decomposition. Others have admitted, in addition 
to vitriolated tartar, the two neutral salts formed by the union of 
the acids of sea-salt [NaCl] and nitre with alkaline fixed bases 
[Na 2 CO 3 , K 2 CO 3 ]; such are sea salt and nitre. Others add 
three more salts formed by the union of the three acids with 


a volatile alkali [ammonium carbonate], viz. Glauber's secret 
ammoniacal salt or vitriolic ammoniacal salt [(NH 4 ) 2 SO 4 ], 
ordinary sal ammoniac [NH 4 C1], and nitrous ammoniacal salt 
[NH 4 NO 3 ]. Other chemists have added several more saline 
substances to the number of these neutral salts. I give to the 
family of neutral salts all the extension of which it is capable ; 
I call a neutral, middle, or salty salt, every salt formed by the 
combination of whatever acid, whether mineral or vegetable, 
with a fixed alkali, a volatile alkali, an absorbent earth [e.g. MgO, 
CaO], a metallic substance, or an oil.' 

Rouelle 's 'neutral' salts were, then, our present 'salts' without 
qualification. He did not leave the matter there, however, but 
went on to divide neutral salts into (a) perfect salts, correspond- 
ing to our 'normal' salts, (b) acid salts and (c) salts with the 
minimum possible acid in them. Perfect salts he defines as 

o 2 

196 Guillaume Franois Rouelle 

those whose point of saturation is exact, and which have the 
exact quantity of acid in them. They do not alter the colour of 
syrup of violets (a contemporary indicator like litmus). Acid 
salts are those which, in addition to the exact quantity of acid 
necessary to give them perfect neutrality, contain a further 
amount. 'And this excess of acid', he says, 'must not be merely 
mixed with the neutral salt ; it must be joined to and combined 
with the other parts, and there must be an exact quantity of it : 
this excess acid itself has its point of saturation/ 

It will be observed that Rouelle had arrived at a scientifically 
sound conclusion as to the formation and classification of salts, 
and that he made our modern distinction between normal (or 
'perfect') and acid salts. He did not quite succeed in defining 
our 'basic' salts, for his third class included such substances as 
silver chloride and calomel, which we now regard as normal 
salts. Rouelle classified them separately on account of their 
sparing solubility; but it was a great advance to recognize that 
they were salts a fact that no one had previously admitted. 

Rouelle was also one of the first to use the word 'base' in 
a sense essentially similar to that which it now bears. Thus he 
says that a salt is to be defined as a substance formed by the 
union of an acid with any substance which serves it as a base and 
gives it a concrete or solid form. 

That his views on the formation and classification of salts 
were established on a firm experimental basis may be gathered 
from the descriptions he gives of properties and preparations. 
He notes, for instance, that acid salts are usually more soluble 
than the corresponding normal salts, and that many of them are 
deliquescent ; that they turn tincture of violets red ; and that 
they cause effervescence with fixed alkalis [K 2 CO 3 and Na 2 CO 3 ] 
and volatile alkali [(NH 4 ) 2 CO 3 ]. Acid potassium sulphate he 
prepared by heating potassium sulphate with sulphuric acid and 
then driving off the excess of acid at a higher temperature. 

Rouelle 's work on salts was not immediately accepted, but 
was revived later by Lavoisier and his school and thus lies at the 
root of our own system. 


46. Summary 

CHEMISTRY under phlogiston was almost entirely qualitative, 
Black's quantitative research upon magnesia alba standing 
nearly alone. The period was one of intense activity, resulting 
in the discovery of scores of new compounds, in the improve- 
ment of laboratory technique, and in the gradual evolution of 
more systematic schemes of classification. The greatest pro- 
gress was, as we have seen, in the chemistry of gases, where 
Priestley, Cavendish and Scheele were daily enlarging the 
hounds of knowledge at a bewildering speed. The phlogiston 
theory throve unchecked, explaining much but leaving many 
things unexplained. No voice was raised against it and it 
numbered among its adherents all the greatest chemists of the 
time. For over half a century it had been 'the lamp and guide of 
chemists', and no one could have foreseen the stirring events 
that were about to happen. 

47. Antoine Laurent Lavoisier 

THE stage is now set for the most dramatic episode in the whole 
story of chemistry: a single-handed, impetuous and determined 
attack on the citadel of phlogiston, ending in its complete over- 
throw and final destruction. Confident in their fancied security, 
the phlogistians at first derided the onslaught, and when at 
length they awoke to the gravity of the position it was already too 
late. Some of them went over to the enemy, but many contested 
the ground inch by inch and fought to the last ditch, but in vain. 
Then, with a gesture of Greek tragedy, Fate ordained the 
political murder of the victor in the very hour of his triumph. 
History offers us few more moving spectacles than that of 
8 May 1794, when the greatest chemist of all time calmly 
awaited death on the guillotine at the hands of the unwashed 
rabble of revolutionary France. 

Antoine Laurent Lavoisier was born of a good family at Paris, 
on 26 August 1743. He and his sister Marie Marguerite Emilie 
were brought up by their maternal grandmother, Madame 
Punctis, for their mother died when the boy was only five years 

198 Antoine Laurent Lavoisier 

old. The Punctis were a wealthy family, and as Lavoisier very 
quickly gave evidence of an unusually high intelligence, they 
lavished money on his education. At the age of 21 he was a 
fully-qualified lawyer, attached to the Parlement, and his relatives 
doubtless foresaw a brilliant legal career for him. Their hopes 


were realized, though not in the sense they expected: Lavoisier 
indeed became a great legislator, but the laws he formulated 
were the laws of chemistry. 

In his hours of leisure, Lavoisier was attracted to the Jardin 
du Roi, where Rouelle J s lectures had inspired Parisian society 
with a passion for chemistry. Every man and woman of fashion 
made a point of attending the laboratory at the Jardin when 
Rouelle was to lecture, and Lavoisier was among their number. 
Another regular auditor was the encyclopaedist Diderot, who 
attended for three years; he was industrious enough to take 
down the lecturer's words and to work them up into a correct 
'edition'. A manuscript copy of Diderot's notes enabled 
Lavoisier to give his full attention to Rouelle and the experi- 
ments, undistracted by the necessity of transferring his impres- 

Antoine Laurent Lavoisier 199 

sions to paper. So was awakened in the young lawyer a deter- 
mination to leave the dust of the law for the study of the 
problems of chemistry: a conversion that was not the least of 
Rouelle's achievements. 

Lavoisier's first chemical paper was published when its 


author was 22. Other researches followed in rapid succession, 
and after a few years he was elected to membership of the 
Academic des Sciences. At about the same time, he became one 
ofihefermiers-gene'rauxywho were responsible for the collection 
of taxes and who, owing to the rapacity and extortion of many 
of their number, were the object of deep-rooted popular hatred. 
There were, of course, honest and conscientious members of the 
ferme, among them Lavoisier, who strove to lessen the cost of 
collecting the taxes and to diminish the severity of the imposts. 
It speaks much for his character that when at length he fell into 
the hands of the revolutionists the only charge they could prefer 
against him was that 'of adding to tobacco water and other in- 
gredients detrimental to the health of the citizens'. 

Before the troublous days of the Revolution, Lavoisier had 

2OO Antoine Laurent Lavoisier 

turned his scientific genius and administrative skill to the benefit 
of his country in several ways. As a member of a Committee of 
Agriculture he worked hard to improve the lot of the French 
agricultural labourer and attempted to introduce scientific 
method into agricultural practice. He was also appointed, by 
Turgot, one of four Commissioners to be directly responsible to 
the State for the manufacture and supply of gunpowder. 

On 1 6 December 1771, Lavoisier married Marie- Anne- 
Pierrette Paulze, a woman who added high intellectual powers 
to a great personal charm. She was able to assist her husband in 
the laboratory, translated the memoirs of Priestley and Caven- 
dish into French, and engraved several plates for a Treatise on 
Chemistry that Lavoisier published in I789. 1 

After Lavoisier had been nominated Commissioner of Powder 
in 1775, he and his wife went to live at the Arsenal, where the 
great discoveries about to be described were made. The labora- 
tory in the Arsenal soon became a rendezvous for French, and 
even foreign, scientists; one might meet there the chemists 
Berthollet, Darcet, Macquer and Guyton de Morveau; the 
mathematicians Laplace and Lagrange; Blagden, permanent 
secretary of the Royal Society ; Benjamin Franklin ; James Watt, 
and the Rev. Joseph Priestley. They were attracted not only by 
the delightful dinners given by M. and Mme Lavoisier, but more 
especially by the 'new and bold' views on the nature of com- 
bustion which their host was now beginning to promulgate. 

About 1770, Lavoisier began an investigation into the 
problems of combustion, and soon discovered that on burning 
sulphur and phosphorus an increase in weight occurs, ac- 
companied by the absorption of much air. Thus when a piece of 
phosphorus was placed under a bell-jar inverted in a trough of 
mercury, and ignited by means of a burning-glass, the following 
observations were made : (i) a limited volume of air will not burn 
an unlimited weight of phosphorus; (2) when an excess of 
phosphorus is used the flame is extinguished after a time, before 

1 After Lavoisier's death, his widow married the American physicist 
Count Rumford. 

Antoine Laurent Lavoisier 201 

the complete combustion of the phosphorus ; (3) to relight the 
residual phosphorus, or to burn a fresh piece, the addition oi 
more air is necessary; (4) a white powder, solid phosphoric acid 
is formed during the combustion ; (5) after the completion of the 
reaction the residual air occupies about four-fifths of the origina! 
volume; (6) the weight of 'phosphoric acid' produced is about 
two and a half times that of the phosphorus taken ; and (7) the 
residual air is slightly lighter than ordinary air, and will nc 
longer support combustion or life. 

Lavoisier followed up this line of experiment by further re- 
searches on the calcination of tin and lead. It will be remembered 
that the increase in weight that occurs when tin and lead are 
burnt had already been observed many times, and was now 
common knowledge. The only explanation that Lavoisier re- 
garded as at all satisfactory was that advanced by Boyle, who 
supposed that heat which he considered a material substance 
had passed through the vessel from the fire to the metal, thus 
causing the increase in weight. Reflection showed, however, 
that this hypothesis was easily susceptible of experimental proof 
or disproof, as Lavoisier most lucidly explains : 

'If, he says, 'the increase in weight of metals calcined in 
closed vessels is due, as Boyle thought, to the addition of the 
matter of flame and fire which penetrates the pores of the glass 
and combines with the metal, it follows that if, after having 
introduced a known quantity of metal into a glass vessel, and 
having sealed it hermetically, one determines its weight exactly; 
and that if one then proceeds to the calcination in a charcoal fire, 
as Boyle did ; and lastly that if one then re weighs the same vessel 
after the calcination, before opening it, its weight ought to be 
found to have increased by the whole of the quantity of the 
matter of fire which entered during the calcination. 

'If, on the contrary . . . the increase in weight of the metallic 
calx is not due to the combination of the matter of fire nor to any 
exterior matter whatever, but to the fixation of a portion of the 
air contained in the space of the vessel, the vessel ought not to 
weigh more after the calcination than before, it ought merely to 

2O2 Antoine Laurent Lavoisier 

be found partly empty of air, and the increase in weight of the 
vessel should take place only at the moment when the missing 
portion of air is allowed to enter/ 

Lavoisier then proceeded to put his views to the test of 
experiment. He took a weighed glass flask, introduced a 
weighed quantity of tin, sealed the flask hermetically and then 
heated it for an hour or two until no further calcination appeared 
to be taking place inside. He now allowed the flask to cool, after 
which he weighed it. There was no change in weight. Upon 
opening the flask, air was heard to rush in, and when the 
apparatus was weighed once more, an increase in weight was 
found. The actual figures obtained in the experiment are as 
follows : 

Onces Gros Grains 

Weight of flask . . . . . 12 6 5175 
Weight of flask plus tin . . . .20 6 

/. Weight of tin . . . . . 8 o 


After calcination but before opening: 
Weight of whole apparatus, unchanged. 

After calcination and opening: 

Onces Gros Grains 

Weight of whole apparatus . . . 20 6 61-81 

/. Increase in weight on calcination o o 10*06 

Lavoisier next removed the tin calx and residual tin from the 
flask and weighed them separately : 

Gros Grains 
Tin calx ...... 











Total weight after calcination 
But total weight before calcination 

/. Increase in weight on calcination . 

These results showed clearly that the increase in weight was 
due, not to the absorption of a hypothetical * matter of fire' as 


Antoine Laurent Lavoisier 203 

Boyle had supposed, but to an absorption of air, the increase in 
weight of the metal being almost exactly equal to the weight of 
air that rushed in when the flask was opened. 

Further experiments on the same lines led him to conclude : 

First, that one cannot calcine an unlimited quantity of tin in 
a given quantity of air ; 

Second, that the quantity of metal calcined is greater in a large 
vessel than in a small one, although it cannot yet be affirmed that 
the quantity of metal calcined is exactly proportional to the 
capacity of the vessels. 

Third, that the hermetically sealed vessels, weighed before and 
after the calcination of the portion of tin they contain, show no 
difference in weight, which clearly proves that the increase in 
weight of the metal comes neither from the material of the fire nor 
from any matter exterior to the vessel. 

Fourth, that in every calcination of tin, the increase in weight of 
the metal is, fairly exactly, equal to the weight of the quantity of 
air absorbed, which proves that the portion of the air which com- 
bines with the metal during the calcination, has a specific gravity 
nearly equal to that of atmospheric air. 

I may add that, from certain considerations drawn from actual 
experiments made upon the calcination of metals in closed vessels, 
considerations which it would be difficult for me to explain to the 
reader without going into too great detail, I am led to believe that 
the portion of the air which combines with the metals is slightly 
heavier than atmospheric air, and that that which remains after the 
calcination is, on the contrary, rather lighter. Atmospheric air, on 
this assumption, would form, relatively to the specific gravity, 
a mean result between these two airs. 

His experimental figures enabled him to deduce that the air 
must consist of at least two gases, only one of which is concerned 
in calcination. By a measurement of the capacity of the flask, he 
was able to calculate the weight of air it originally contained. 
This was considerably greater than the weight of air that 
entered when the flask was opened, the deduction therefore 
being that only a part of the air had been used. Now, since 
there was an excess of tin, the cessation of calcination before the 

204 Antoine Laurent Lavoisier 

whole of the air had been consumed could be explained only on 
the assumption that the air consists of a mixture of gases, of 
which one can effect calcination while the other or others cannot. 

At this point occurred the pregnant meeting with Priestley, 
who described his amazing experiment with mercury calx. 
Lavoisier immediately appreciated the importance of Priestley's 
discovery, and at once became convinced that 'dephlogisticated 
air' was in reality the active constituent of the atmosphere 
that constituent absorbed by metals on calcination. During the 
winter of 1774-5 ne repeated and extended Priestley's experi- 
ments, and described his results to the Academic des Sciences 
early in the latter year. 

He first showed that by heating red calx of mercury with 
carbon one obtained mercury and 'fixed air', and secondly, that 
by heating the red calx alone Priestley's 'dephlogisticated air' 
was evolved. From one ounce of the calx he obtained 78 cubic 
inches of the latter gas, and showed that it did not turn lime- 
water milky (as fixed air does), that it would not combine with 
alkalis, that it was able to bring about the calcination of metals, 
and that it supported life and combustion very well 'tous les 
corps combustibles en general s'y consommaient avec une eton- 
nante rapidite'. It is evident that his observations were practically 
those of Priestley, but his conclusions were very different: 

It thus appears to be proved that the principle which combines 
with metals during their calcination, and which increases their 
weight, is nothing else than the purest portion of the very air which 
surrounds us, which we breathe, and which passes, during this 
operation [i.e. calcination], fromt he gaseous state to the solid state; 
if, therefore, one obtains it in the form of fixed air in all metallic 
reductions where carbon is used, this effect is due to the combina- 
tion of the carbon with the pure portion of the air. It is, indeed, 
very probable that all metallic calces would, like that of mercury, 
give nothing but l eminently respirable air' if one could reduce 
them all without the addition of any other substance, as one 
reduces red precipitate of mercury per se. 

His crucial experiment, however that which has come to be 

Antoine Laurent Lavoisier 


known as 'Lavoisier's Experiment 'par excellence we may allow 
him to relate in his own words : 

I took a matrass [A, Fig. 68] of about 36 cubical inches capacity, 
having a long neck BCDE, of six or seven lines internal diameter, 
and having bent the neck as in [Fig. 68], to allow of its being 
placed in the furnace MM/V7V, in such a manner that the extremity 


of its neck E might be inserted under a bell-glass /*'G, placed in 
a trough of quicksilver RRSS\ I introduced four ounces of pure 
mercury into the matrass, and, by means of a syphon, exhausted 
the air in the receiver FG, so as to raise the quicksilver to /,/,, and 
I carefully marked the height at which it stood, by pasting on a slip 
of paper. Having accurately noted the height of the thermometer 
and barometer, I lighted a fire in the furnace MMNN, which 
I kept up almost continually during twelve days, so as to keep the 
quicksilver always very near its boiling-point. Nothing remarkable 
took place during the first day: the mercury, though not boiling, 
was continually evaporating, and covered the interior surface of the 
vessel with small drops, at first very minute, which gradually 
augmenting to a sufficient size, fell back into the mass at the bottom 
of the vessel. On the second day, small red particles began to 
appear on the surface of the mercury; these, during the four or five 
following days, gradually increased in size and number, after which 
they ceased to increase in either respect. At the end of twelve days, 
seeing that the calcination of the mercury did not at all increase, 
I extinguished the fire, and allowed the vessels to cool. The bulk 

206 Antoine Laurent Lavoisier 

of air in the body and neck of the matrass, and in the bell-glass, 
reduced to a medium of 28 inches of the barometer and 54-5 of the 
thermometer, at the commencement of the experiment was about 
50 cubical inches. At the end of the experiment the remaining air, 
reduced to the same medium pressure and temperature, was only 
between 42 and 43 cubical inches; consequently it had lost about 
J of its bulk. Afterwards, having collected all the red particles, 
formed during the experiment, from the running mercury in which 
they floated, I found these to amount to 45 grains. 

I was obliged to repeat this experiment several times, as it is 
difficult in one experiment both to preserve the whole air upon 
which we operate, and to collect the whole of the red particles, or 
calx of mercury, which is formed during the calcination. It will 
often happen in the sequel, that 1 shall, in this manner, give in one 
detail the results of two or three experiments of the same nature. 

The air which remained after the calcination of the mercury in 
this experiment, and which was reduced to of its former bulk, 
was no longer fit either for respiration or for combustion; animals 
being introduced into it were suffocated in a few seconds, and when 
a taper was plunged into it, it was extinguished as if it had been 
immersed in water. 

In the next place I took 45 grains of red matter formed during 
this experiment, which I put into a small glass retort, having 
a proper apparatus for receiving such liquid, or gaseous product, 
as might be extracted. Having applied a fire to the retort in the 
furnace, I observed that, in proportion as the red matter became 
heated, the intensity of its colour augmented. When the retort was 
almost red hot, the red matter began gradually to decrease in bulk, 
and in a few minutes after it disappeared altogether; at the same 
time 41 J grains of running mercury were collected in the recipient, 
and 7 or 8 cubical inches of elastic fluid, greatly more capable of 
supporting both respiration and combustion than atmospherical 
air, were collected in the bell-glass. 

A part of this air being put into a glass tube of about an inch 
diameter, showed the following properties: A taper burned in it 
with a dazzling splendour, and charcoal, instead of consuming 
quietly as it does in common air, burnt with a flame, attended with 
a decrepitating noise, like phosphorus, and threw out such a 
brilliant light that the eyes could hardly endure it. This species 

Antoine Laurent Lavoisier 207 

of air was discovered almost at the same time by Dr. Priestley, 
Mr. Sheele, and myself. Dr. Priestley gave it the name of de- 
phlogisticated air, Mr. Sheele called it empyreal air ; at first I named 
it highly respirable air y to which has since been substituted the term 
of vital air. We shall presently see what we ought to think of these 

In reflecting upon the circumstances of this experiment, we 
readily perceive, that the mercury, during its calcination, absorbs 
the salubrious and respirable part of the air, or, to speak more 
strictly, the base of this respirable part ; that the remaining air is 
a species of mephitis, incapable of supporting combustion or 
respiration ; and consequently that atmospheric air is composed of 
two elastic fluids of different and opposite qualities. As a proof of 
this important truth, if we recombine these two elastic fluids, 
which we have separately obtained in the above experiment, viz. 
the 42 cubical inches of mephitis, with the 8 cubical inches of 
respirable air, we reproduce an air precisely similar to that of the 
atmosphere, and possessing nearly the same power of supporting 
combustion and respiration, and of contributing to the calcination 
of metals. 

Lavoisier had thus by now begun to elaborate an entirely new 
theory of combustion, and had shown (i) that air consists of at 
least two gases, one of which, 'air eminemment respirable' 
(Priestley's dephlogisticated air), combined with metals on cal- 
cination and thus caused the increase in weight, (2) that the 
same air was the active agent in combustion, (3) that 'fixed air' 
(carbon dioxide) was a compound of charcoal with this air, and 
(4) that metallic calces were not elements, as had previously been 
thought, but compounds of the metals with 'eminently respir- 
able air'. His position was therefore incompatible with the 
phlogiston theory, and in 1783 he attacked the theory in his 
Reflexions sur Phlogistique. In the intervening years he had 
continued his researches and had discovered that the combin- 
ation of moist 'eminently respirable air' with sulphur yielded 
sulphuric acid, with phosphorus phosphoric acid, with nitrogen 
nitric acid, and with carbon carbonic acid. Hence, he says, 
'I shall for the future call dephlogisticated air or eminently 

208 Antoine Laurent Lavoisier 

respirable air by the name of the acidifying principle, or, if the 
same meaning is preferred in a Greek word, by that of the 
oxygine principle', thus bestowing upon the gas its modern 
name, oxygen. 

'In designing the word Oxygen ', says Professor H. E. Arm- 
strong, ' Lavoisier rose to the greatest height of his unparalleled 
genius. Not only is the word a monument to his astounding 
insight into chemical phenomena, to his philosophic power; it is 
also proof of a deep philological feeling and acumen, as well as of 
his sense of the beauty of words. Think of the astounding step 
he took, after his instant appreciation of Priestley's discovery, in 
translating the old nonconformist's ponderous reminder of the 
doubtful past of our science conveyed in the name Dephlogisti- 
cated Air into an all-significant word of the aural and lingual 
perfection of Oxygen . . . think of him as the pioneer who not 
only sought to put system into the souls of chemists but also 
tipped their tongues with harmony.' 

Meanwhile the phlogistians were beginning to pass from 
amusement to alarm. Lavoisier's audacity in casting a doubt 
upon the theory of phlogiston had at first provoked sarcasm 
and heavy humour. The Grand Master of French phlogistian 
chemistry, Macquer (professor at t\\ejardin du Roi), refers with 
scorn to 'a certain person who wishes to meddle in higher 
chemistry without understanding anything of the science', and 
in 1778 writes as follows to Guy ton de Morveau: 

M. Lavoisier has been terrifying me for some time by a great dis- 
covery, which ke kept in petto and which was going to do no less 
than to overthrow the theory of phlogiston ; his confident air nearly 
made me die of fright. Where should we have been, with our old 
chemistry, if we had had to build an entirely different edifice ? For 
my own part, I don't mind admitting I should have given up the 
game. However, M. Lavoisier has just published this discovery 
of his, and I can tell you that since that time I have had a great 
weight removed from my chest. 

Scheele was equally sceptical. * Would it be so difficult', he 
wrote to the chemist Bergman in 1784, 'to convince Lavoisier 

Antoine Laurent Lavoisier 209 

that his system of acids [i. e. that they are compounds of oxygen] 
is not to everybody's taste ? Nitric acid composed of pure air 
and nitrous air [NO 2 ], aerial acid [CO 2 ] of carbon and pure air, 
sulphuric acid of sulphur and pure air! ... Is it credible ? . . . 


1. Calcination. 

2. Constitution of calx. 

3. Increase in weight on 


4. Mercury calx yields 

'pure air' when 

5. Calx heated with 

charcoal yields 
metal and fixed air. 

6. Phlogiston cannot be 


Water can be made 
by exploding a 
mixture of 'dephlo- 
gisticated' and 'in- 
flammable' airs. 

A flame in a limited 
volume of air is 
soon extinguished. 

Why does not air 
saturated with 
phlogiston become 
inflammable ? In 
point of fact it is 
not inflammable. 

| Phlogistian Explanation. \ Lavoisier's Explanation. 

Gain of oxygen. 
Metal -f oxygen. 
Due to weight of oxygen 

taken up. 
Oxygen is liberated from 

the metallic oxide. 

Loss of phlogiston. 
Metal phlogiston. 
Pnlogiston has nega- 
tive weight. 
(See p. 176.) 

Charcoal yields phlo- 
giston to calx. 

Heat, light, and mag- 
netism and electri- 
city cannot be iso- 

Dephlogisticated air 
is water deprived of 

The air becomes satu- 
rated with phlogis- 

No explanation offer- 

Charcoal combines with 
oxygen in calx, forming 
'carbonic acid gas' and 
leaving the metal. 

It does not exist. 

Water is a compound of 
oxygen and inflam- 
mable air [hydrogen]. 

The oxygen in the air is 
all consumed. See 
no. 9. 

'Air saturated with phlo- 
giston' is merely air 
that has lost its 
oxygen but is other- 
wise unchanged ; there 
is therefore no reason 
why it should become 

I will rather place my faith in what the English say [i.e. Priestley, 
Cavendish, and others].' 

Cavendish, on the contrary, was cautious, and admits that his 
own experiments, as well as 'most other phaenomena of nature, 
seem explicable as well, or nearly as well, upon Lavoisier's 

2613-4 P 

2i o Antoine Laurent Lavoisier 

theory as upon the commonly believed principle of phlogiston'. 
Priestley, however, was adamant in his refusal to see any 
blemishes in the phlogiston theory or any good points in that of 
Lavoisier, and the general situation began to change in favour of 
Lavoisier only in 1785. Yet if we compare the explanations of 
certain common phenomena given by the phlogiston theory and 
the oxygen theory respectively, we shall not be surprised to find 
that defection from the former, once started, soon became 
general, except for one or two older men such as Priestley. For 
the sake of clearness, the facts and their interpretations may be 
tabulated (see previous page). 

Heedless of his initial lack of success, Lavoisier renewed the 
attack, armed with clear ideas and incontestable facts; his on- 
slaught soon became irresistible. 

It is time [he says] to recall chemistry to a more rigorous method 
of reasoning; to strip the facts with which this science is enriched 
every day from that which reasoning and prejudices add thereto; 
to distinguish fact and observation from that which is systematic 
and hypothetical; finally, to mark the limit, so to speak, to which 
chemical knowledge has arrived, in order that those who follow us 
may set out with confidence from this point to advance the science. 
Chemists have made of phlogiston a vague principle which is 
not rigorously defined, and which consequently adapts itself to all 
explanations into which it may be brought. Sometimes this 
principle is heavy, and sometimes it is not ; sometimes it is free fire, 
sometimes it is fire combined with the earthy element ; sometimes 
it passes through the pores of vessels, and sometimes they are 
impenetrable for it. It explains at once causticity and non- 
causticity, transparency and opacity, colours and the absence of 
colours. It is a veritable Proteus which changes its form at every 

He proceeds to demonstrate, with sure logic, how the oxgyen 
theory satisfactorily explains the known facts of combustion, and 
how the phlogiston theory fails. Phlogiston is 'an imaginary 
entity', and the relevant facts can be explained much more 
simply without it than with it. Yet Lavoisier realized the great 

Antoine Laurent Lavoisier 211 

hold that the phlogiston theory had on the minds of men, and 
concludes his memoir by saying: 

I do not expect that my ideas will he adopted all at once; the 
human mind adjusts itself to a certain point of view, and those who 
have looked at nature from one standpoint, during a portion of 
their life, adopt new ideas only with difficulty; it is, then, for time 
to confirm or to reject the opinions which I have brought forward. 
Meanwhile, I see with a great satisfaction that young people who 
begin to study the science without prejudice, that mathematicians 
and physicists who come fresh to chemical truths, no longer believe 
in phlogiston in the way in which Stahl presented it, and look upon 
the whole of this doctrine as a scaffolding more embarrassing than 
useful for the continuance of the structure of chemical science. 

Lavoisier was, however, too pessimistic about the attitude of 
contemporary chemists, for on 6 August 1785, Berthollet swore 
allegiance to the new theory ; de la Metherie, Monge, Guyton de 
Morveau and Fourcroy soon followed ; and in 1791 Kirwan, one 
of the staunchest English protagonists of phlogiston, wrote : 'At 
last I am laying down my arms and abandoning phlogiston. 
I see clearly that there is no authentic experiment in which the 
production of fixed air from pure inflammable air has been 
demonstrated, and that being so, it is impossible to maintain the 
system of phlogiston. ... I myself will give a refutation of my 
own essay on phlogiston/ 

Priestley alone remained obdurate. One of the last acts of his 
life (he died in 1804) was to issue a Defence of Phlogiston, in 
which he reiterates his faith in the system of Stahl, and remarks 
that it appears 'not a little extraordinary, that a theory so new, 
and of such importance, overturning everything that was thought 
to be best established in chemistry, should rest on so very 
narrow and precarious a foundation; the experiments adduced 
in support of it being not only ambiguous, or explicable on 
either hypothesis, but exceedingly few. . . . Tho' the title of this 
work expresses perfect confidence in the principles for which 
I contend, I shall still be ready publicly to adopt those of my 
opponents, if it appears to me that they are able to support them. 


212 Antoine Laurent Lavoisier 

Nay, the more satisfied I am at present with the doctrine of 
phlogiston, the more honourable shall I think it to give it up 
upon conviction of its fallacy : following the noble example of 
Mr. Kirwan, who has acquired more honour by this conduct 
than he could have done by the most brilliant discoveries that he 
could have made/ 

As Priestley's splendid but lonely figure disappears over the 
horizon, the old theory vanishes for ever. It was a great and 
brilliant theory and served chemistry well : the reader will there- 
fore feel a peculiar pleasure in learning that the victors always 
spoke of it with respect. One of them truly remarked that 'it 
made chemistry a new science by the precision of its luminous 
ideas', and that its simple and easy principles had long been 
a compass to guide the path of each and every chemist. 

The new theory was firmly established by 1792. Lavoisier 
fully appreciated the value of his own work. Although he was 
not altogether scrupulous in assigning due credit to others, he is 
at pains to have it clearly understood that to him and to him 
alone is due the honour of founding the oxygen theory. 

This theory is not, as I have heard it called, the theory of the 
French chemists in general, it is mine, and it is a possession to 
which I lay claim before my contemporaries and before posterity. 
Others, no doubt, have given it new degrees of perfection, but 
I hope that one will not be able to deny to me the whole theory of 
oxidation and combustion; the analysis and decomposition of air 
by metals and combustible bodies ; the theory of the formation of 
acids; more exact knowledge of a great number of acids, notably 
vegetable acids; the first ideas on the composition of plant and 
animal substances, and the theory of respiration. 

This claim may be fully admitted, and it is pleasant to know 
that Lavoisier was spared for a short time to enjoy his triumph. 
But Fate had already marked him down, and on 8 May 1794 the 
usher of the revolutionary tribunal handed in the following report : 

I have been to the prison of the tribunal for the execution of the 
judgement pronounced to-day against Lavoisier, condemning him 
to death, after which I handed him over to the responsible official 

The Revision of Nomenclature 213 

and to the gendarmerie, who took him to the Place de la Revolution 
[now Place de la Concorde'], where, upon a scaffold erected upon 
the said Place, the aforesaid Lavoisier, in my presence, suffered the 
pain of death. 

La Republique ria pas besoin de savants, said the cynical 

Fig. 69. C. L. BERTHOLLET 

Coffinhal, president of the tribunal. But Lagrange, with 
saddened insight, voiced the later feelings of the whole French 
people when he said, // ne leur a fallu quun moment pour fairs 
tomber cette tete, et cent annees peut-etre ne suffiront pas pour en 
reproduire une semblable. 

48. The Revision of Nomenclature 

THE complete revolution in fundamental chemical principles 
effected by Lavoisier made the old system or rather lack of 
system of nomenclature obsolete. A new scheme, in con- 
sonance with the oxygen theory, was urgently necessary if the 
progress of chemistry was to be unhindered by relics of its 
'doubtful past*. Lavoisier realized this fact very clearly, and, in 
conjunction with three of his disciples, Guyton de Morveau, 

214 The Revision of Nomenclature 

Berthollet and Fourcroy, he undertook the elaboration of a 
nomenclature based upon scientific principles. Guy ton de Mor- 
veau had already before his conversion to the oxygen theory 
attempted to reform the old nomenclature, and was thus in 
a position to realize its main defects. He pointed out (a) that 
a chemical name should not be a phrase, (b) that it ought not to 
require circumlocutions to become definite, (r) that it ought to 
recall the constituents of a compound body, (d) that it should 
not be of the type 'Glauber's salt', which conveys nothing about 
the composition of the substance, (e) that in the absence of 
knowledge concerning the constitution of a substance, the name 
should be non-committal, (/) that new names should preferably 
be coined from Latin or Greek, so that their signification could 
the more widely and easily be understood, and (g) that the form 
of such words should be assimilated to the genius of the language 
in which they are to be used. De Morveau's advice and ex- 
perience must have proved extremely valuable to Lavoisier and 
the other two members of the committee of nomenclature. 

The results of prolonged conferences between this committee 
and other scientists whose advice they sought were published in 
1787 under the title Methode de Nomenclature Chimique. In a 
prefatory memoir, Lavoisier observes that there are three things 
to distinguish in every physical science : the series of facts that 
constitute the science, the ideas that recall the facts, and the 
words that express them. The word must evoke the idea, the 
idea must depict the fact : they are but three impressions of the 
same seal. The perfect chemical nomenclature would render 
ideas and facts in their exact verity, without suppression and 
more particularly without addition ; it ought to be nothing more 
than a faithful mirror. It is obvious, he says, that the language of 
chemistry as it then existed had not been formed on those 
principles; indeed, it could not have been. Moreover, some 
chemical expressions were introduced by the alchemists, and 
bore one meaning for the adept but another for the vulgar ; thus, 
'a pelican' represented an apparatus for distillation, while caput 
mortuum signified the residue from a distillation. 'Oil', ' mercury ', 

The Revision of Nomenclature 215 

and even ' water' were not oil, mercury, and water in the sense in 
which we employ the words; and so on. 

Equally objectionable, he maintains, are such names as powder 
ofAlgaroth, salAlembroth, turbith mineral, colcothar, and aethiops, 
which make excessive demands upon the memory and give no 
information about the substances for which they are employed. 
More ridiculous still are 'oil of vitriol 5 , 'oil of tartar by delique- 
scence', 'butter of arsenic', 'flowers of zinc', 'liver of sulphur', 
'sugar of lead', &c., which actually give rise to wrong impres- 
sions and (as Dumas remarked later) make one think that the 
chemists have borrowed their language from the kitchen. 

Guy ton de Morveau followed Lavoisier's memoir with another 
in which he showed how the principles laid down could be 
applied. The system suggested is essentially that which we now 
employ, and it is therefore unnecessary for us to consider it in 
detail. Our present purpose will be served by a consideration of 
a typical example. Sulphur, says de Morveau, in combining 
with oxygen produces an acid. It is evident that, to conserve the 
idea of this origin and to express clearly the first degree of com- 
position, the name of this acid ought to be a derivative of the 
name of its basis ; but this acid exists in two states of saturation, 
and shows different properties in each. In order not to confuse 
them, each state must be given a name which, while conserving 
the primitive root, nevertheless marks this difference. Lastly, it 
is necessary to consider sulphur in other direct combinations, 
e.g. with alkalis, earths and metals. Five different terminations, 
adapted to the same root, in the manner which has appeared 
most convenient by the judgement of the ear, distinguish the 
five states of one principle : 

Sulphuric acid will express sulphur saturated with oxygen as 
far as it can be; i.e. what is called vitriolic acid. 

Sulphurous acid will express sulphur united to a less quantity 
of oxygen; i.e. what is called volatile sulphurous vitriolic 

Sulphate will be the generic name of all salts formed from 
sulphuric acid. 

2i6 The Revision of Nomenclature 

Sulphite will be the name of salts formed from sulphurous 

Sulphide will denote all compounds of sulphur not carried to 

the state of an acid, and will thus replace, in a uniform 

manner, the improper and varying names of 'liver of 

sulphur', 'hepar', 'pyrites', &c. 

He adds with justice that 'no one will fail to perceive, at the first 
glance, all the advantages of such a nomenclature, which, while 
indicating various substances, at the same time defines them, 
recalls their constituent parts, classes them in their order of 
composition, and to a certain extent draws attention to the 
proportions that cause the variation in their properties'. 

The work of the committee was completed by a dictionary 
giving the new and old names of about 700 substances, in which 
we find for the first time many very familiar words sulphuretted 
hydrogen, copper nitrate, ammonium molybdate, zinc sulphate, 
and so on. The enormous improvement of the new system over 
the old may be gathered from a single instance : that of the sub- 
stance which Lavoisier and his collaborators proposed to call 
carbonate of potash. Previously, this compound had rejoiced in 
no fewer than eight aliases, viz. sal fixe de tartre, alkali fixe 
vegetal, alkali fixe vegetal aere, tartre crayeux, tartre mephitique, 
mephite de potasse, nitre fixe par lui-meme, alkaest de Vanhel- 
mont! 'Potassium carbonate' may not be as picturesque as 'nitre 
fixed by itself or 'van Helmont's alcahest', but few chemists 
will be inclined to regret the passing of the old nomenclature. 
As an appendix to the Methode de Nomenclature Chimique, 
Hassenfratz and Adet wrote a memoir on a proposed system of 
symbols for use in chemistry, to replace the old alchemical and 
pharmaceutical ones. Non-metallic elements were to be repre- 
sented by straight lines and semicircles, while the symbols for 
metals were to be circles enclosing the initial letters of their 
names. Symbols for compounds were to be formed by putting 
together the symbols of their components . While this system had 
its advantages, it was too complicated to win general approval 
and was never widely adopted. We shall find shortly that the 

Sir Isaac Newton 217 

whole question of chemical symbolism was about to be placed 
on an entirely new footing by the development of the Atomic 
Theory. It is to this theory, with all its tremendous con- 
sequences, that we must now turn. 

49. Sir Isaac Newton 

IT is a significant coincidence that the year 1804, which witnessed 
the death of the last supporter of the Aristotelian Elements the 
chemist Baume should also have seen the first effective use in 
chemistry of the Greek theory of atoms . In the eighteen hundred 
years that had elapsed since the days of Lucretius, the atomic 
conception of matter underwent little development and re- 
mained a subject for the speculation of philosophers rather than 
a tool for the advancement of science. Towards the close of the 
period, indeed, it seems to have been almost entirely neglected, 
when attention was once more focused on it by the celebrated 
dispute between Descartes (1596-1650) and Gassendi (1592- 
1655). Gassendi stoutly supported the atomic theory of 
Epicurus, while Descartes, though not an extreme anti-atomist, 
argued against the classical form of the theory with an eloquent 
lucidity. It is unnecessary to observe that discussions of this 
kind, however great their subsequent influence on the general 
philosophic scheme, have very little direct value to a particular 
science. Nothing more was known about the structure of matter 
when Gassendi and Descartes had concluded their controversy 
than before it had begun ; and the historian of science is bound 
to feel a sympathy with the caustic words of Omar Khayyam 
himself a mathematician and astronomer 

Myself when young did eagerly frequent 

Doctor and saint, and heard great argument 

About it and about: but evermore 

Came out by the same door as in I went. 

Yet we should guard against the easy assumption that pure 
philosophy may be regarded as of little worth from the point of 
view of pure science ; nothing could be farther from the truth. 
Mr. Cyril Bailey has said with justice that 'it was the Greeks 

2i 8 Sir Isaac Newton 

who put the questions which modern science is still endeavour- 
ing to answer', and one may extend this thesis : philosophy in 
general puts the grand questions and suggests possible answers. 
It is for the scientist to decide what questions are susceptible of 
complete or partial solution by the methods at his disposal. The 


important conclusion that emerges from this digression is that 
the theories of science are the products of the scientist, and that 
we must neither belittle philosophy for failing to do what lies 
outside its province, nor give the scientist less than justice in 
regarding his theories as mere plagiarisms. 

The immediate service that Descartes and Gassendi rendered 
to chemistry was that they brought the atomic hypothesis into 
such prominence that no chemist could remain in ignorance 
of it. We find evidence of this fact in the writings of Boyle, 
who refers to the 'corpuscular theory' in a way which implies 
that it was perfectly familiar to his contemporaries; and it 
gained further consideration from scientists when Sir Isaac 
Newton (1642-1727) declared his allegiance. Newton's support 
was of particular importance, for although his fame rests mainly 
upon his physical and mathematical discoveries, he was a keen 
student of chemical phenomena and theories. He had a 
laboratory at Cambridge, in 'the space between the road and the 

Sir Isaac Newton 219 

college on the right-hand side on entering the Great Gate at 
Trinity College', and we are told that for 'about 6 weeks at 
spring and 6 at ye fall, ye fire in the elaboratory scarcely went 
out, which was well furnished with chymical materials as bodyes, 
receivers, heads, crucibles, &c., which was made very little use 


of, ye crucibles excepted, in which he fused his metals ; he would 
sometimes, tho' very seldom, look into an old mouldy book 
which lay in his elaboratory. I think it was titled Agricola de 
Metallis y the transmuting of metals being his chief design*. 
His library contained a large number of books on chemistry, and 
he corresponded on chemical subjects with Boyle and Locke and 
with the former's assistant, Hooke. 

In his Opticks, Newton says: 'It seems probable to me that 
God in the beginning formed matter in solid, massy, hard, im- 
penetrable, moveable particles, of such sizes and figures, as most 
conduced to the end for which He formed them ; and that these 

22O Sir Isaac Newton 

primitive particles , being solids , are incompara bly harder than any 
porous bodies compounded of them ; even so very hard as never 
to wear or break in pieces, no ordinary power being able to 
divide what God Himself made one in the first creation. . . . God 
is able to create particles of matter of several sizes and figures, 
and in several proportions to the space they occupy, and perhaps 
of different densities and forces. . . . Now, by the help of these 
principles, all material things seem to have been composed of the 
hard and solid particles above mentioned variously associated 
in the first creation, by the counsel of an intelligent agent/ 

This passage is very reminiscent of Lucretius, but Newton 
was a scientist and applied his hypothesis to experimental fact. 
Boyle had recently discovered his 'Law', and Newton offered 
a theoretical explanation of the phenomenon in 'the first 
quantitative conclusion ever formed about atoms'. He proved in 
the Principia that 'if the density of a fluid gas which is made up 
of mutually repulsive particles is proportional to the pressure, 
the forces between the particles are reciprocally proportional to 
the distances between their centres. And vice versa, mutually 
repulsive particles, the forces between which are reciprocally 
proportional to the distances between their centres, will make 
up an elastic fluid, the density of which is proportional to the 
pressure/ Newton goes on: 'Whether elastic fluids do really 
consist of particles so repelling one another, is a physical 
question. We have here demonstrated mathematically the pro- 
perties of fluids consisting of this kind, that hence philosophers 
may take occasion to discuss that question/ 

What strikes us immediately is the great difference in attitude 
towards the atomic theory, between the scientists as exemplified 
by Newton and the general body of atomic philosophers. It 
is perfectly true to say that the atomic theory can be traced, in 
unbroken historical continuity, from Leucippus to Newton, but 
Newton's position is this: 'Let us suppose that these are atoms 
and see what may be deduced therefrom in accordance with ex- 
perimental fact', and therein lies the vital difference between 
a scientific theory and a philosophic speculation. 

John Dalton 221 

Newton's suggestion that a gas may be composed of particles 
that repel one another in a perfectly definite way was the 
immediate cause of the formulation of the chemical atomic 
theory a century later. 


5- John Dalton 

IN the Introductory Discourse to his Dictionary of Chemistry, 
the French chemist Wurtz exclaimed with pardonable pride, 
Chemistry is a French science. It was founded by Lavoisier, of 
immortal memory. An Englishman may yield to none in his 
admiration of Lavoisier's work, but will claim that the great 
Frenchman found an equal in the humble Quaker schoolmaster 
John Dalton. Dalton was the son of a weaver, and was born at 
Eaglesfield in Cumberland about 6 September 1766. As his 
parents were poorly off, he had to begin to earn his own living at 
the early age of 12, and in 1785 he and his brother Jonathan 

222 John Dalton 

opened a school at Kendal, where, says the prospectus, 'Youth 
will be carefully instructed in English, Latin, Greek, French; 
also Writing, Arithmetic, Merchants' Accompts, and the Mathe- 
matics'. The school was not generally popular, 'owing to the 
uncouth manners of the young masters, who did not seem to 
have had much intercourse with society; but John's natural dis- 
position being gentler, he was more passable'. The boys in 
particular preferred John, because he was so absorbed in his 
mathematics that their faults escaped notice. 

In 1793 Dalton was appointed tutor in mathematics and 
natural philosophy at the Manchester Academy, a continuation 
of the similar establishment at Warrington, with which, it will 
be remembered, Priestley had been connected for some time. 
Dalton remained at the Academy for six years, after which he 
resigned his post and became a private tutor, devoting all his 
leisure hours to scientific research. Modest in his requirements, 
and simple and regular in his habits, Dalton lived a quiet and 
unassuming life even when in after years he had acquired a 
European reputation. Sir Henry Roscoe relates that in 1826, 
when the fame of the Quaker scientist was at its height, 
*M. Pelletier, a well-known Parisian savant , came to Manchester 
with the express purpose of visiting the illustrious author of the 
Atomic Theory. Doubtless, he expected to find the philosopher 
well known and appreciated by his fellow citizens probably 
occupying an official dwelling in a large national building 
devoted to the prosecution of science, resembling, possibly, his 
own College de France or Sorbonne. There he would expect to 
find the great chemist lecturing to a large and appreciative 
audience of advanced students. What was the surprise of the 
Frenchman to find, on his arrival in Cottonopolis, that the 
whereabouts of Dalton could only be found after diligent search ; 
and that, when at last he discovered the Manchester philosopher, 
he found him in a small room of a house in a back street, engaged 
looking over the shoulders of a small boy who was working his 
"cyphering" on a slate. "Est-ce que j'ai Thonneur de m'ad- 
dresser a M. Dalton?" for he could hardly believe his eyes that 

John Dalton 223 

this was the chemist of European fame, teaching a boy his first 
four rules. "Yes," said the matter-of-fact Quaker. "Wilt thou 
sit down whilst I put this lad right about his arithmetic?" ' 

Through a fondness for meteorology, Dalton was led to a 
study of the properties and composition of the atmosphere and 


Rcfpc&fufly inform their Friends, and the Public in genera), that they intend to continue 
the SCHOOL lately feogbt by 


Where Youth will be carefully inftru&ed in 

Englifh, Latin, Greek, and French J 

A I 8 O 

Writing, Arithmetic Merchants Accompts, 

The School to be opened on the 28th of March, 1785 

N. B. Youth boarded in the Matter** Houfe on reafonable 


thence to an investigation of 'elastic fluids' or gases in general. 
Steeped in the works of Newton, he habitually thought in terms 
of atoms, and the atomic theory seems to have first taken shape 
in his mind as a physical theory to explain the properties of gases. 
'Having long been accustomed to make meteorological observa- 
tions/ he said, 'and to speculate upon the nature and constitu- 
tion of the atmosphere, it often struck me how a compound 
atmosphere, or a mixture of two or more elastic fluids, should 
constitute apparently a homogeneous mass, or one in all 
mechanical relations agreeing with a simple atmosphere. 
Newton had demonstrated clearly in the 23rd. Prop, of Book II 

224 John Dalton 

of the Principia that an elastic fluid is constituted of small 
particles or atoms of matter which repel each other by a force 
increasing in proportion as their distance diminishes.' 

Applying Newtonian principles to the problem of mixed gases, 
he was able to account for a phenomenon he had observed in 
1 80 1, viz. that the pressure in a mixture of gases is the sum of 
the partial pressures, or that in such a mixture each gas exerts 
the same pressure as it would if it were separately enclosed in 
the volume occupied by the whole mixture. This he explained 
by assuming that when two gases, 'denoted by A and 5, are 
mixed together, there is no mutual repulsion amongst their 
particles, that is, the particles of A do not repel those of B, as 
they do one another'. Although this explanation is no longer 
held, it shows that Dalton was already employing an atomic 
hypothesis, and that he was profoundly influenced by the ideas 
of Newton. Two years later, Dalton was able to publish his Law 
of Partial Pressures, which states that if a mixture of gases is 
exposed to a liquid, each gas dissolves in the liquid according to 
its partial pressure. 

The further sequence of events which led to the enunciation of 
the chemical atomic theory is not clear, owing to contradictory 
accounts given by Dalton himself, his friend Thomas Thomson, 
and the various notebooks and other documents preserved in 
Dalton's laboratory at 36, George Street, Manchester. However, 
on 26 August 1804, Dalton gave an account of his views on the 
composition of matter to Thomson, who incorporated them in 
the third edition of his System of Chemistry (1807). Thomson 
took notes at the time, and the reproduction of them he gives in 
his History of Chemistry is quoted here. The views they contain 
were afterwards amplified by Dalton and published in his New 
System of Chemical Philosophy, to which we shall return later. 

The ultimate particles of all simple bodies are atoms incapable of 
further division. These atoms . . . are all spheres, and are each of 
them possessed of particular weights, which may be denoted by 
numbers. For the greater clearness Mr. Dalton represented the 
atoms of the simple bodies [elements] by symbols. The following 

Ai^S^co l^ff-rt^^f^->^-<^ ^^v~-4-s 

CH \~4t**^fS-.- 



226 John Dalton 

are his symbols for four simple bodies, together with the numbers 
attached to them by him in 1804: 




Azote [nitrogen] 

Relative Weights 

O 6-5 

O i-o 


CD 5-o 


The following symbols represent the way in which he thought 
these atoms were combined to form certain binary compounds, 
with the weight of an integrant particle of each compound : 

GO Water ....... 7-5 

0O Nitrous gas [nitric oxide] . . . * 11-5 

00 Olefiant gas [ethylene] . . . . 6-0 

O Ammonia ...... 6-0 

O0 Carbonic oxide [carbon monoxide] . . 11-5 

The following were the symbols by which he represented the 
composition of certain tertiary compounds : 

O0O Carbonic acid [carbon dioxide] 

(DO Nitrous oxide 

O0 O Carburetted hydrogen [methane] 

OCDO Nitric acid [nitrogen peroxide] 




John Dalton 227 

Thomson was very much attracted by Dalton's scheme, and 
lost no time in drawing the attention of other chemists to it. 

There were, however, some of our most eminent chemists who 
were very hostile to the atomic theory. The most conspicuous of 
these was Sir Humphry Davy. In the autumn of 1807 I had a long 
conversation with him at the Royal Institution, but could not con- 


vince him that there was any truth in the hypothesis. A few days 
after, I dined with him at the Royal Society Club, at the Crown and 
Anchor, in the Strand. Dr. Wollaston was present at the dinner. 
After dinner every member of the club left the tavern, except 
Dr. Wollaston, Mr. Davy, and myself, who staid behind and had 
tea. We sat about an hour and a half together, and our whole con- 
versation was about the atomic theory. Dr. Wollaston was a con- 
vert as well as myself; and we tried to convince Davy of the in- 
accuracy of his opinions; but, so far from being convinced, he 
went away, if possible, more prejudiced against it than ever. Soon 
after, Davy met Mr. Davis Gilbert, the late distinguished president 
of the Royal Society; and he amused him with a caricature de- 
scription of the atomic theory, which he exhibited in so ridiculous 
a light, that Mr. Gilbert was astonished how any man of sense or 


228 John Dalton 

science could be taken in with such a tissue of absurdities. 
Mr. Gilbert called on Dr. Wollaston (probably to discover what 
could have induced a man of Dr. Wollaston's sagacity and caution 
to adopt such opinions), and was not sparing in laying the 
absurdities of the theory, such as they had been represented to him 
by Davy, in the broadest point of view. Dr. Wollaston begged 


Mr. Gilbert to sit down, and listen to a few facts which he would 
state to him. He then went over all the principal facts at that time 
known respecting the salts ; mentioned the alkaline carbonates and 
bicarbonates, the oxalate, binoxalate, and quadroxalate of potash, 
carbonic oxide and carbonic acid, olefiant gas and carburetted 
hydrogen; and doubtless many other similar compounds, in which 
the proportion of one of the constituents increases in a regular 
ratio. Mr. Gilbert went away a convert to the truth of the atomic 
theory ; and he had the merit of convincing Davy that his former 
opinions on the subject were wrong. What arguments he employed 
I do not know ; but they must have been convincing ones, for Davy 
ever after became a strenuous supporter of the atomic theory. 






Printed by S. Russell, isj, Deansgatc, 

Fig. 78 

230 John Dalton 

While the theory was taking shape, Dalton obtained much 
assistance in clarifying his views by an investigation of the con- 
stitution of olefiant gas [ethylene] and carburetted hydrogen 

It was obvious from the experiments which he made upon them, 
that the constituents of both were carbon and hydrogen, and 
nothing else. lie found further, that if we reckon the carbon in 
each the same, the carburetted hydrogen gas contains exactly 
twice as much hydrogen as olefiant gas- docs. This determined him 
to state the ratios of these constituents in numbers, and to con- 
sider the olefiant gas as a compound of one atom of carbon and one 
atom of hydrogen; and carburetted hydrogen of one atom of 
carbon and two atoms of hydrogen. The idea thus conceived was 
applied to carbonic oxide, water, ammonia, etc. ; and numbers 
representing the atomic weights of oxygen, azote, etc., deduced 
from the best analytical experiments which chemistry then 

By 1808 his ideas had become quite precise, and in that year 
he published the first part of his great book A New System of 
Chemical Philosophy. Throughout this work the atomic theory 
is constantly used, and the main points in it are emphasized. 
These may be shortly stated as follows : 

1. All matter is composed of a great number of extremely 
small particles or atoms. To attempt to conceive the number of 
particles is like attempting to conceive the number of stars in the 
universe ; we are confounded by the thought. But if we limit the 
subject, by taking a given volume of a gas, we seem persuaded 
that, let the divisions be ever so minute, the number of particles 
must be finite ; just as in a given space of the universe, the number 
of stars and planets cannot be infinite. 

2. Chemical analysis and synthesis go no farther than to the 
separation of particles one from another, and to their reunion. 
In other words, atoms are indestructible and cannot be created, 
whence may be deduced the Law of the Conservation of Matter, 
viz. matter can neither be created nor destroyed. 'No new 
creation or destruction of matter is within the reach of chemical 
agency. We might as well attempt to introduce a new planet 

John Dalton 231 

into the solar system, or to annihilate one already in existence, 
as to create or destroy a particle of hydrogen. All the changes 
we can produce consist in separating particles that are in a state 
of cohesion or combination, and joining those that were pre- 
viously at a distance.' 

3. Each element has its own distinctive kind of atom, and 
similarly each compound has its own distinctive kind of 'com- 
pound atom' or ultimate mechanical particle. Thus, any one 
atom of iron exactly resembles any other atom of iron, but is 
different from the atoms of all other elements ; and all 'com- 
pound atoms' of water exactly resemble one another but differ 
from the 'compound atoms' of all other compounds. 

4. It is important, and possible, to ascertain the relative weights 
of different atoms. 'In all chemical investigations, it has justly 
been considered an important object to ascertain the relative 
weights of the simples [elements] which constitute a compound. 
But unfortunately the inquiry has terminated here; whereas, 
from the relative weights, the relative weights of the ultimate 
particles or atoms of the bodies might have been inferred, from 
which their number and weight in various other compounds 
would appear, in order to assist and to guide future investiga- 
tions, and to correct their results. Now it is one great object of 
this work, to show the importance and advantage of ascertaining 
the relative weights of the ultimate particles, both of simple and 
compound bodies, the number of simple elementary particles 
which constitute one compound particle, and the number of less 
compound particles which enter into the formation of one more 
compound particle.' 

5. When elements combine to form compounds, the ultimate 
particles of the compounds consist of small whole numbers of 
the atoms of the elements concerned. Thus if there are two 
elements A and B, which are disposed to combine, the following 
is the order in which the combinations may take place, beginning 
with the most simple : 

i atom of A + 1 atom of B = i ultimate particle of C, a binary 

232 John Dalton 

1 atom of A +2 atoms of B = i ultimate particle of D, a 
ternary compound. 

2 atoms of A + i atom of B i ultimate particle of E, a 
ternary compound. 

i atom of ^[+3 atoms of B --- i ultimate particle of F, a 
quaternary compound. 

3 atoms of A-\-i atom of B =- i ultimate particle of G y a 
quaternary compound. 

At this stage Dalton had no means of determining the actual 
numbers of atoms in the ultimate particles of compounds, so 
that he had to fall back on assumptions. The main assumptions 
that he made were these : 

i st. When only one combination [compound] of two elementary 
bodies can be obtained, it must be presumed to be a binary one, 
unless some cause appear to the contrary. 

2nd. When two combinations are observed, they must be 
presumed to be a binary and a ternary. 

3rd. When three combinations are obtained, we may expect one 
to be a binary, and the other two ternary. 

4th. When four combinations are observed, we should expect 
one binary, two ternary, and one quaternary, etc. 

7th. The above rules and observations apply, when two com- 
pound bodies, such as C and D, D and E, etc., are combined. 

These postulates were obviously the most suitable ones to 
make, since they were the most readily tested by quantitative 
experimental work; they could easily be modified in particular 
cases if the results of analysis so required. 

Dalton next proceeded to put his principles into practice, and 
showed how the relative weights of the atoms of different 
elements might be determined. His method may be illustrated 
by the following examples : 

i . Water. At that time only one compound of hydrogen and 
oxygen was known, namely water. Analysis showed that in 
water eight parts by weight of oxygen were combined with one 
of hydrogen. But since no other compound of hydrogen and 

John Dalton 233 

oxygen was known, water was considered to be a binary compound, 
that is, to be composed of one atom of each element. Hence 
the oxygen atom must be eight times as heavy as that of hydrogen. 

2. Ammonia. This was the sole compound of nitrogen and 
hydrogen known to Dalton, who therefore regarded it as a 
binary compound, composed of one atom of each element. By 
analysis it was found that the relative weights of hydrogen and 
nitrogen in ammonia were as i is to about 5, hence the nitrogen 
atom must weigh about five times as much as that of hydrogen. 

3. Carbon oxides. Dalton knew of two oxides of carbon, 
carbonic oxide [carbon monoxide] and carbonic acid [carbon di- 
oxide] ; the former he considered to be a binary compound of one 
atom of carbon and one of oxygen, and the other a ternary com- 
pound of one atom of carbon and two of oxygen. By quantita- 
tive analysis it was therefore easy to arrive at the relative weights 
of the oxygen and carbon atoms. 

Working in this way Dalton was able to construct a table of 
atomic weights of the elements, that is, their relative weights 
taking the weight of the hydrogen atom as unity. The following 
are the numbers he gives in one place : 

Atomic Atomic 

Element Weight Element Weight 

Hydrogen i Zinc .... 56 

Azote [nitrogen) . . 5 Copper . . . .56 

Carbon .... 5 Lead 95 

Oxygen .... 7 Silver .... 100 

Phosphorus ... 9 Platinum . . 100 

Sulphur . . .13 Gold .... 140 

Iron . . . .38 Mercury . . .167 

In the same way he was able to discover the relative weights, 
compared to the hydrogen atom, of ultimate particles of com- 
pounds, e.g. : Weight of iji timate 

Compound Particle 








234 John Dalton 

A glance at the above tables will show that Dalton 's values are 
in many cases very different from those accepted at the present 
day. This is partly due to inaccurate analysis, but a little con- 
sideration will make it apparent that the real difficulty lay in the 
fact that Dalton had no conclusive means of arriving at the 
number of atoms in the ultimate particle of any compound. 
Thus he assumed, in the absence of evidence to the contrary, 
that the ultimate particle of water contains only i atom of 
hydrogen and i of oxygen, and hence obtained, by deduction 
from the data supplied by quantitative analysis, the number 8 
for the atomic weight of oxygen. It is, however, obvious that if 
the ultimate particle of water consists of 2 atoms of hydrogen and 
i of oxygen, then the atomic weight of the latter will be 16, 
while if it consists of 3, 4, 5, &c., atoms of hydrogen and i of 
oxygen, the atomic weight of oxygen must be 24, 32, 40, &c. 
In the same way, by regarding the ultimate particle of 
ammonia to consist of i atom of hydrogen and i of nitrogen, 
Dalton obtained * about 5' for the atomic weight of nitrogen, 
instead of the modern value 14 which is based upon the 
fact that i molecule or ultimate particle of ammonia consists 
of i atom of nitrogen combined with not i but 3 atoms of 

This lack of knowledge of the number of atoms in the ultimate 
particle of a compound was a serious hindrance to the develop- 
ment of the theory. Dalton himself was fully alive to the 
difficulty, and even as late as 1827 expresses himself as quite 
frankly dissatisfied with the position. 'The second object of the 
atomic theory/ he writes, 'namely, that of investigating the 
number of atoms in the respective compounds, appears to me to 
have been little understood, even by some who have undertaken 
to expound the principles of the theory.' 

When two bodies, A and J5, combine in multiple proportions; 
for instance, 10 parts of A combined with 7 of B to form one 
compound, and with 14 to form another, we are directed by some 
authors to take the smallest combining proportion of one body as 
representative of the elementary particle or atom of that body. 

John Dalton 235 

Now it must be obvious to anyone of common reflection, that such 
a rule will be more frequently wrong than right. For, by the above 
rule, we must consider the first of the combinations as containing 
i atom of B and the second as containing 2 atoms of B, with 

1 atom or more of A ; whereas it is equally probable by the same 
rule that the compounds may be 2 atoms of A to i of B y and i 
atom of A to i of B respectively; for, the proportions being 10 A 
toy B (or, which is the same ratio, 20 A to 14 B) and 10 A to 14 B, 
it is clear by the rule, that when the numbers are thus stated, we 
must consider the former combination as composed of 2 atoms of 
A, and the latter of i atom of A, united to i or more of B. Thus 
there would be an equal chance for right or wrong. But it is 
possible that 10 of A, and 7 of B, may correspond to i atom ^4,and 

2 atoms B ; and then 10 of A, and 14 of B, must represent i atom 
A y and 4 atoms B. Thus it appears the rule will be more 
frequently wrong than right. It is necessary not only to consider 

the combination of A with B y but also those of A with C\ D,E> , 

before we can have good reason to be satisfied with our determina- 
tions as to the number of atoms which enter into the various com- 
pounds. Elements [compounds] formed of azote [nitrogen] and 
oxygen appear to contain portions of oxygen, as the numbers 1,2, 
3, 4, 5 successively, so as to make it highly improbable that the 
combinations can be effected in any other than one of two ways. 
But in deciding which of those two we ought to adopt, we have to 
examine not only the compositions and decompositions of the 
several compounds of these two elements, but also compounds 
which each of them forms with other bodies. I have spent much 
time and labour upon these compounds, and upon others of the 
primary elements, carbon, hydrogen, oxygen, and azote, which 
appear to me to be of the greatest importance in the atomic 
system; but it will be seen that I am not satisfied on this head, 
either by my own labour or that of others, chiefly through want of 
an accurate knowledge of combining proportions. 

How the difficulty was at length overcome we shall see in 
succeeding pages. Meanwhile, we may turn to some of the 
deductions that can be made from Dalton's atomic theory and 
learn of their fate in the crucible of experiment. The chief of 
these deductions are familiar to every student of chemistry 

236 John Dalton 

under the title of the Laws of The Conservation of Matter, 
Constant Composition, Multiple Proportions and Reciprocal 

The Law of the Conservation of Matter states that matter can 
neither be created nor destroyed. When early chemists thought 
about this problem, which was seldom, they seem to have 
assumed the impossibility of creating or destroying matter ; but 
it was only with the gradual introduction of quantitative method 
during the eighteenth century, by men like Black, Lavoisier and 
others, that the question really became urgent. By that time, 
however, the rational habit of thought had so far taken possession 
of chemists that the conservation of matter was never seriously 
doubted ; Lavoisier tacitly assumes it in all his experiments but 
never troubles to give formal expression to such an obvious 
truism. It will be at once apparent that the Law of the Con- 
servation of Matter is a corollary of the atomic theory, for if 
atoms are uncreatable and indestructible, matter composed of 
them must possess the same characteristics. In ordinary 
chemical reactions, the most accurate quantitative analysis has 
never been able to detect any exceptions to this law. 

The Law of Constant Composition states that any particular 
compound has an invariable composition. This directly follows 
from the atomic theory, since if all the ultimate particles of a 
compound are identical, as Dalton postulated, they must contain 
the same numbers of the same kinds of atoms, and all the atoms 
of the same element are , ex hypothesi, identical . Lavoisier appears 
to have taken this law, like that of the Conservation of Matter, 
as axiomatic; but his fellow-countryman Berthollet, in a book 
entitled Essai de Statique Chimique, maintained that variable 
composition is the rule and constant composition the exception. 
He urged that only in particular cases and under special condi- 
tions do elements and compounds combine in fixed proportions. 
Berthollet was opposed by Proust (1755-1826), who was able to 
prove, by exact quantitative analysis, that numerous compounds 
obeyed the law with extreme accuracy, and that Berthollet had 
confused true chemical compounds with mixtures or solutions 

John Dalton 237 

of which the composition may be continuously variable within 
certain limits. 

According to my view [said Proust], a compound is a privileged 
product to which nature has assigned a fixed composition. Nature 
never produces a compound even through the agency of man, 
other than balance in hand, ponder e et mensura. Between pole and 
pole compounds are identical in composition. Their appearance 
may vary owing to their mode of aggregation, hut their properties 
never. No differences have yet been observed between the oxides 
of iron from the South and those from the North ; the cinnabar of 
Japan has the same composition as the cinnabar of Spain; silver 
chloride is identically the same whether obtained from Peru or 
from Siberia; in all the world there is but one sodium chloride; 
one saltpetre; one calcium sulphate; and one barium sulphate. 
Analysis confirms these facts at every step. 

The second deduction from the atomic theory was thus found 
to be in accordance with experimental fact ; and subsequent re- 
search has supplied overwhelming confirmation of its truth. 

The Law of Multiple Proportions states that when two elements 
combine together to form more than one compound, then the 
weights of one of those elements which combine with a fixed 
weight of the other are in a simple ratio to one another. Like 
the two preceding laws, this third law is a logical inference from 
the atomic theory. Suppose, for example, that the elements A 
and B unite together to form two different compounds. The 
simplest imaginable case will be when in one of the compounds 
the ultimate particle consists of one atom of A and one of 5, and 
in the other compound the ultimate particle consists of one 
atom of A and two of B. Since, in one ultimate particle of each 
of these two compounds there is one atom of A, it follows that 
the weight of A is constant in the two particles. The weights of 
B, on the other hand, will be in the ratio of the numbers of 
atoms of B respectively present in the particles; in this instance, 
1:2. This is a simple ratio, and if compounds are always com- 
posed of small numbers of atoms, the ratio will always be a ratio 
of small numbers and therefore a simple one. 

Although Dalton never gave this law formal expression, there 

238 John Dalton 

is no doubt whatever that he thoroughly understood it. Indeed, 
from the table given on p. 226, which dates from 1804, we can 
gather that he already knew of several instances in which the law 
held good, viz., carbonic oxide (CO) and carbon dioxide (CO 2 ) ; 
olefiant gas (C 2 H 4 ) and carburetted hydrogen (CH 4 ); and 
nitrous gas (NO), nitrous oxide (N O) and 'nitric acid' (NO 2 ). 
Further confirmation was forthcoming in 1808, when Thomson 
analysed the two oxalates of potassium (KHC 2 O 4 and K 2 C 2 O 4 ) 
and showed that one contains 'just double the proportion of 
base' contained in the other. In the same year, Wollaston 
pointed out that similar relations held in the cases of the car- 
bonates and bicarbonates, and sulphates and bisulphates, adding 
that all the facts he had observed were 'but particular instances 
of the more general observation of Mr. Dalton, that in all cases 
the simple elements of bodies are disposed to unite atom to 
atom singly, or if either is in excess, it exceeds by a ratio to be 
expressed by some simple multiple of the number of its atoms'. 
With sudden insight, he foreshadows an important later develop- 
ment of chemical theory: 'I am further inclined to think, that 
when our views are sufficiently extended to enable us to reason 
with precision concerning the proportions of elementary atoms, 
we shall find the arithmetical relation alone will not be sufficient 
to explain their mutual action, and that we shall be obliged to 
acquire a geometrical conception of their relative arrangement 
in all the three dimensions of solid extension.' Wollaston's 
prophecy was fulfilled in 1875, when van't Hoff initiated the 
study of the arrangement of atoms in space. 

The complete establishment of the Law of Multiple Propor- 
tions was effected by the Swedish chemist Johann Jacob Berze- 
lius (1779-1848) who, in the years 1808-12, analysed with ad- 
mirable accuracy a vast number of salts and other compounds. 
His analytical figures were such that he was enabled to write to 
Dalton: 'You are right in this, that the theory of multiple pro- 
portions is a mystery without the atomic hypothesis : and as far 
as I have been able to see, all the results gained hitherto con- 
tribute to justify this hypothesis/ 

John Dalton 239 

The Law of Reciprocal Proportions, also a logical deduction 
from the theory, states that if an element A combines with an 
element B and also, separately, with an element C, then if B and 
C also combine together, the proportion by weight in which they 
do so will be simply related to the ratio of the weights of B and 
C which combine, separately of course, with a constant weight 
of A. The necessity of this relation will be obvious when it is 
remembered that Dalton postulated (a) that combination takes 
place between small numbers of atoms, to form the ultimate 
particles of compounds, and (b) that all the atoms of the same 
element are of exactly the same weight. Particular instances of 
the law were observed by Richter (1762-1807), but it was again 
Berzelius who thoroughly established it. 

All the principal deductions from Dalton 's theory were thus 
found to be in perfect agreement with experimental evidence, 
and general acceptance of the theory quickly followed. The 
scientific world hastened to shower honours upon its illustrious 
author. In 1822 he was elected a Fellow of the Royal Society; 
in 1830 the French Academy of Sciences made him a Foreign 
Associate, 'the highest station it has to bestow, and universally 
regarded as the crowning distinction in European science'. At 
the meeting of the British Association at Oxford in 1832, the 
honorary degree of D.C.L. was conferred upon him, and the 
story goes that he proudly wore his scarlet gown (the colour of 
which he could not appreciate, as he was colour-blind) through 
the streets. In 1833 the Government conferred upon Dalton 
a Civil List pension of 150, afterwards raised to 300, and the 
next year he had the honour of being presented to the King. In 
1837 his health began to fail, and he was seized with a slight 
attack of paralysis, from which he never completely recovered. 
A further attack gave warning of its approach on 26 July 1844; 
on the following day 'his housekeeper found him in a state of 
insensibility, and before medical attendance could be procured, 
though it was immediately sent for, he expired, passing away 
without a struggle or a groan, and imperceptibly, as an infant 
sinks into sleep*. 

240 Jbterzelms 

So died 'the framer of a theory with respect to the mode of 
combination between bodies, which stands foremost among the 
discoveries of the present age for the universality of its applica- 
tions and the importance of its practical results, holding the 
same kind of relation to the science of chemistry which the 
Newtonian system does to that of mechanics; and throwing 
light, not only upon all the ordinary subjects of chemical in- 
vestigation, but even upon those more speculative questions, 
with respect to the constitution of matter, which seemed to lie 
beyond the reach of experimental inquiry'. 

51. Berzelius 

THOUGH Dalton enunciated the Atomic Theory, it was Berzelius 
who did more than any other chemist to provide it with a sound 
basis of accurate experimental fact. Two of his services to the 
theory we have just learnt, but that which is perhaps the greatest 
has yet to be described. Let us, however, first satisfy our natural 
curiosity as to the personality of this great ' Maker of Chemistry', 
who for many years ruled the chemical world with a rod of iron : 
as, indeed, well he might, for the name Berzelius means 'the man 
of iron', or so the etymologists suggest. 

Berzelius was born at Wafnersunda, in Sweden, on 20 August 
1779. His father was head-master of a school in the neighbour- 
ing town of Linkoeping. At the local Gymnasium, Berzelius 
appears to have shown but little promise, for his leaving certifi- 
cate remarked that he 'justified only doubtful hopes'; and his 
examiners at Upsala, where he studied medicine, were totally 
unimpressed by his chemical ability. In 1802, however, he 
sprang at once into fame, on the publication of some brilliant 
chemical researches, and was immediately appointed assistant 
professor of chemistry and pharmacy in the medical school at 
Stockholm: a new post that was actually created for him. 
Five years later he was made full professor, retaining this office 
for a quarter of a century. In 1818, King Karl Johann raised 
him to the rank of nobleman, and on the occasion of his marriage, 
in 1835, he was made a baron. 

Berzelius 241 

Berzelius 's private laboratory at Stockholm soon became the 
goal of young chemists ; to work with the great master was their 
highest ambition. One of them, Wohler, who himself afterwards 
became famous, has left us a vivid picture of his first impressions : 


As he [Berzelius] led me [said Wohler] into his laboratory I was, 
as it were, in a dream, doubting whether it was really true that I 
was in this famous place. Adjoining the living-room, the labora- 
tory consisted of two ordinary chambers with the simplest fittings ; 
there was neither oven nor fume chamber, neither water nor gas 
supply. In one room stood two ordinary work-tables of deal ; at 
one of these Berzelius had his working-place, the other was assigned 
to me. On the walls were several cupboards with reagents which, 
however, were not provided very liberally, for when I wanted 
prussiate for my experiments I had to get it from Liibeck. In the 
middle of the room stood the mercury trough and glass-blower's 
table, the latter under one of the chimney-places provided with 

2613-4 R 

242 Berzelius 

a curtain of oiled silk. The washing place consisted of a stone 
cistern having a tap with a pot under it. In the other room were the 
balances and other instruments, besides a small work-bench and 
lathe. In the kitchen, where the food was prepared by the severe 
old Anna, cook and factotum of the master who was still a bachelor, 
stood a small furnace and the ever-heated sandbath. 

Anna's dual responsibilities, as cook and laboratory assistant, 
must have proved heavy especially as Berzelius seems to have 
insisted upon keeping her chemistry up-to-date. On one 
occasion, after Davy had shown that the gas hitherto called 
oxymuriatic acid, and supposed to be a compound, was really an 
element to which he gave the name chlorine, Berzelius overheard 
Anna grumbling about the smell of 'oxymuriatic acid' in a flask 
she was washing. 'Hearest thou, Anna 7 ; he reproved her, 'thou 
must no longer speak of oxidised muriatic acid ; thou must call it 
chlorine: that is better!' 

As an experimental chemist, Berzelius was nearly, if not quite, 
the equal of his fellow-countryman Scheele. His work, however, 
lay on different lines, and was chiefly concerned with the develop- 
ment of comprehensive and accurate schemes of qualitative and 
quantitative analysis. Having established the schemes, he 
employed them to test the accuracy of the laws of chemical com- 
bination and more particularly to determine atomic weights. 
The results he obtained are in many cases astonishingly close 
to those now accepted, and offer a striking illustration of his 
experimental skill. Berzelius 's figures did more than anything 
else to ensure the universal adoption of the atomic theory; 
but his supreme achievement was the establishment of the 
present system of chemical notation. If we reflect for a moment 
upon the convenience of our symbols, formulae and equations, 
upon the continual use we make of them, and upon the concise, 
definite information they contain, we shall realize how vitally 
important they are, and how difficult chemistry would be with- 
out them. Essential as they are at the present day, their impor- 
tance in the early days of the atomic theory was even more 
fundamental, for they enabled the rank and file of the army of 

Berzelius 243 

chemists to think in terms of atoms. Great philosophic minds 
might perhaps have applied the atomic theory to chemical 
problems without the assistance of literal symbols ; but we are 
not all cast in this heroic mould. The conceptions of the theory 
are, at bottom, highly abstruse, and the triumph of Berzelius is 

n. B M E N T S 

O O 

9 in II 13 U I* 

<D> <fl> O O 

H 18 19 00. 





that he rendered those conceptions intelligible to every one of us 
through his scheme of symbolic representation. 

The story of chemical symbolism is a long one, reaching back 
to the very origins of chemistry itself. Sometimes the symbols 
were used to convey information, sometimes to conceal it except 
from the initiated ; sometimes they were purely practical, and at 
others they served to express mystical ideas in alchemical terms. 

R 2 

244 Berzelius 

Until the end of the eighteenth century, however, there was no 
serious attempt at the construction of a systematic and uniform 
scheme which should serve the sole purpose of a concise expres- 
sion of chemical facts. Hassenfratz and Adet and others then 
attacked the problem in a careful and logical fashion, but the 
matter was soon afterwards raised to a higher plane by the 
arrival of the atomic theory. 

The first scheme of atomic notation was introduced by Dalton 
himself, who used circles with lines and dots as symbols for the 
atoms of elements, and appropriate groupings of these elemen- 
tary symbols as formulae for the ultimate particles of compounds. 
A list of some of Dalton 's symbols and formulae is given in 
Fig. 80. The important difference between Dalton J s symbols and 
those which had been used in earlier times is this : that whereas 
the old sign $, for instance, had signified copper in any quantity , 
Dalton 's symbol Q stood for one atom of copper, and thus 
possessed a definite quantitative significance completely absent 
from the sign 5. The formulae of compounds conveyed even 
more information; thus that of carbon dioxide, O0O, showed 
that, in the opinion of those who adopted it, i ultimate particle 
of carbon dioxide contains i atom of carbon and 2 of oxygen ; 
and since (according to Dalton) the atomic weight of oxygen is 
6-5 and that of carbon 5, the formula implicitly states that the 
composition by weight of carbon dioxide is carbon : oxygen as 

5 ' 13- 

Dalton's formulae were adopted by those few chemists who 

fully appreciated their tremendous import, but for the chemical 
world in general the system proved much too cumbersome. 
Fortunately, about 1814 or even a little earlier, Berzelius 
suggested an incomparably more convenient notation, which is, 
in essentials, the one that we now employ. In his Thdorie des 
Proportions Chimiques (first edition, 1819; second edition, 1835), 
he points out that the use of symbols greatly facilitates the ex- 
pression of chemical facts. In order to render the usage general, 
it would be quite sufficient to give each body its own particular 
sign, which would represent the relative weight of its atom. 

Berzelius 345 

'We have chosen as the symbols for bodies the initial letters of 
their Latin names/ he says. 'When the names of the several 
bodies have the same initial, one adds the first letter which is not 
common to them. For example, C signifies Carbon, Cl = 
Chlorine, Cr == Chromium, Cu = Copper, Co = Cobalt. No 
letter is added to the initials of non-metals, even when their 
names begin with the same letters as those of certain metals ; 
from this rule, however, chlorine, bromine and silicon must be 
excepted, since their names have the same initials as those of the 
other non-metals carbon, boron and sulphur. 

'The number of atoms is indicated by figures. A figure on the 
left multiplies all the atoms placed on its right, as far as the 
first + or the end of the formula. A little figure placed to the 
right of the letter, above, like an algebraic exponent, multiplies 
solely those atomic weights on the immediate left. Thus S 2 O 5 
indicates an atom [ultimate particle] of hyposulphuric acid, and 
2 S 2 O 5 indicates two atoms of the same acid. . . . Here are the 
symbols for each element : 

H Hydrogen 
N Nitrogen 
S Sulphur 

P Phosphorus 

Cl Chlorine 

Br Bromine 

1 Iodine 
Pt Platinum 
Pd Palladium 
Hg Mercury 
Ag Silver 

Cu Copper 

U Uranium 

Bi Bismuth 

Sn Tin 

Pb Lead 

F Fluorine 

C Carbon 

Ta Tantalum 

Ti Titanium 

Os Osmium 

Au Gold 

Ir Iridium 

R Rhodium 

Te Tellurium 

Co Cobalt 

Ni Nickel 

Fe Iron 

M Manganese 

Ce Cerium 

Al Aluminium 

Zr Zirconium 

Th Thorium 

246 Berzelius 

Cd Cadmium Y Yttrium 

Zn Zinc G Glucinum [beryllium] 

B Boron Mg Magnesium 

Si Silicon Ca Calcium 

Se Selenium Sr Strontium 

As Arsenic Ba Barium 

Cr Chromium L Lithium 

Mo Molybdenum Na Sodium (natrium) 

W Tungsten (wolfram) K Potassium (kalium).' 

Sb Antimony (stibium) 

It will be observed that Berzelius 's list is practically identical 
with ours, very few changes (except additions) having been made 
since the publication of the original. Both his symbols and his 
formulae, indeed, were so simple to use, so easy to remember, 
and so concisely informative, that they very quickly gained 
universal currency. There were a few malcontents, among 
them Dalton. ' Berzelius 's symbols are horrifying/ he wrote to 
Graham in 1837, 'a young student in chemistry might as soon 
learn Hebrew as make himself acquainted with them. They 
appear like a chaos of atoms. Why not put them together in 
some sort of order? Is not the allocation a subject of investiga- 
tion as well as the weight? If one order is found more consistent 
than another, why not adopt it till a better is found? Nothing 
has surprised me more than that such a system of symbols should 
ever have obtained a footing anywhere/ Elsewhere he says, 
'I do not, however, approve of his adopting and defending the 
chemical symbols of Berzelius, which appear to me equally to 
perplex the adepts of science, to discourage the learner, as well 
as to cloud the beauty and simplicity of the atomic theory.' 

Berzelius 's reply to his critics was dignified and convincing: 

May I be allowed to reply to some objections which have been 
made to the use of these formulae for the designation of the atomic 
composition of bodies ? It has been said that they lack clearness, 
induce error, and offer no advantage. Surely, they are obscure 
only as long as one is unfamiliar with their meaning; once one 
knows how to interpret them, nothing can be easier than to under- 

Berzelius 247 

stand them. In no case can they lead to error, for they are simply 
the expression of the composition of a substance, according to the 
opinion of him who constructed the formula. If this opinion is 
incorrect, it will lead to error, in whatever manner it is expressed ; 
the formula in itself contributes nothing to the error. It has also 
been said that these formulae produce a disagreeable impression 
upon the mathematicians, because the number, known in algebra 
as the exponent and placed above to the right, has a greater value 
than in these formulae, and that above all one should recognize the 
rights of the mathematicians; such an objection is not worth 
refuting. The letter P has the value of an R in the Greek and 
Russian languages; and, in reading a book, it is not more probable 
that in reading, say, Russian, one would be deceived over the 
significance of this letter, than that one would be deceived, in 
a chemical work, by taking a chemical sign for an algebraic formula. 
In the one case, the use of letters and numbers is based upon 
principles different from those in the other ; for there is no reason 
why they should be the same. As far as concerns the objection of 
uselessness, it will suffice to give one example, to prove how much 
may be expressed by these formulae, and how clear the expression 
is: KOSO 3 +A1 2 O 3 3SO 3 + 24H 2 O is ... the formula which ex- 
presses the composition of alum. It shows that in this salt one 
atom of potassium is combined with 2 atoms of aluminium, 4 
atoms of sulphur, 48 atoms of hydrogen, and 40 atoms of oxygen; 
that one atom of potash is combined with one atom of alumina, 
4 atoms of sulphuric acid, and 24 atoms of water, or that an atom of 
potassium sulphate is combined with an atom of aluminium 
sulphate. . . . One may say it is true, that most of these data are the 
immediate consequences the ones of the others : doubtless that is 
so for those who know these consequences, but for them the word 
alum says as much as the whole formula ; the latter 's object is, then, 
to give with ease a summary of that which one should observe. 

Berzelius 's last sentence gives the raison d'etre of the modern 
formula, which expresses, in an extremely condensed form, that 
information about a chemical compound which the chemist 
regards as the most important. The system of notation has been 
modified and extended since the time of Berzelius, but his con- 
ception of a formula as a summary of experience still holds good. 

248 Avogadro 

By a mere inspection of its formula, a chemist may gather as 
much about the constitution, preparation, properties and re- 
actions of a substance as from several pages of prose description. 
Chemical symbols are still a language 'not understanded of the 
people', but to the chemist they are the chief medium of the 
expression and transmission of knowledge. 

52. Avogadro 

ALTHOUGH Dalton's arguments and Berzelius's data were 
successful in establishing the atomic theory, they failed to re- 
move the fundamental difficulty to which reference has already 
been made : that of discovering with certainty the number of 
atoms in the ultimate particle of a substance. Both Dalton and 
Berzelius attempted to take the position by flank attacks, for 
they perceived its vital importance ; but their efforts were fruit- 
less, and many chemists did not hide their belief that the problem 
was insoluble. They had good reason to assume this attitude, 
for it must have appeared quite hopeless to expect ever to 
obtain a definite knowledge of the architecture of such minute 
objects as the ultimate particles of matter. 

The most that quantitative analysis could yield at that time 
was the combining proportion of an element, or that number 
which we now call its equivalent. By a consideration of various 
fragments of incidental evidence, it was possible in certain cases 
to reach a shrewd idea of the structure of the particles of the 
substance under investigation, but in no single instance could 
the result be taken as final. Early lists of 'atomic weights' are 
therefore essentially lists of equivalents, though in many in- 
stances collateral data demanded that the equivalent of an 
element should be multiplied by some small whole number 
a procedure that was duly carried out in compiling the list. It is 
obvious that as long as atomic weights were uncertain, very 
little progress could be made in discovering the domestic 
arrangements of the atoms within the ultimate particle of a 
compound, as even the number of these atoms could not be 
definitely settled. 

Avogadro 249 

The glory of having shown how this grievous difficulty could 
be overcome belongs to the Italian scientist Avogadro, a worthy 
product of the country of Galileo and Leonardo. What greater 
tribute to his genius could we pay than to emphasize the fact 


that where those giants of chemistry, Dalton and Berzelius, 
failed, Avogadro triumphed? 

Lorenzo Romano Amedeo Carlo Avogadro, Count of Quaregna 
and Cerreto, was born in Turin on 9 August 1776. The name 
Avogadro is a corruption of Avvocato, a barrister, and recalls the 
fact that Avogadro's ancestors had been advocates in ecclesias- 
tical courts. Avogadro was himself trained for the courts as a 
young man, and in 1796 was given the degree of doctor of 
ecclesiastical law. From 1800-5, however, he assiduously studied 
mathematics and physics, for which he had a deep predilection, 
and on 7 October 1809, he was nominated Professor of these 
subjects at the Royal College at Vercelli. In November 1820 

250 Avogadro 

King Victor Emanuel I established a chair of mathematical 
physics in the University of Turin, and Avogadro became the 
first professor. He held this post until July 1822 and again from 
1834 until 1850, when he retired. 

Avogadro married Donna Felicita Mazze di Biella, 'with 
whom he shared for more than forty years the cares and joys of 
life'. He had two sons: Luigi, who became a general in the 
Italian army, and Felice, who, at the time of his death, was 
President of the Court of Appeal. 

As to his personal character, we are told that Avogadro was 
'religious without intolerance, learned without pedantry, wise 
without ostentation, a despiser of pomp, without care for riches, 
not ambitious for honours ; ignorant of his own worth and fame, 
modest, temperate, and lovable'. He died in 1856, after the 'life 
of a philosopher of the ancient type, occupied wholly with his 
studies, while not forgetting his duties as a citizen and father of 
a family*. His features, as rendered by his portraits, well express 
the charm of his character ; one feels that the eulogies just quoted 
must have been fully justified. 

Avogadro was a staunch adherent of the atomic theory, almost 
from the moment of its publication, and was quick to perceive 
its fundamental defect. How he was led to his brilliant hypo- 
thesis which, as Nernst truly remarked, has proved to be 'a horn 
of plenty* to chemistry, we shall discover by a consideration of 
Gay-Lussac's work on gases. 

Joseph-Louis Gay-Lussac (1778-1850) was a celebrated 
French chemist, who became Professor of Chemistry at the 
Jardin des Plantes, and was later made a peer of France. As 
a man he is said to have been cold and reserved, but his private 
life was not without its romance, as the following anecdote 
(related by Sir William Tilden) will show : 

At the beginning of the Revolution in 1789 there lived at Auxerre 
a musician attached to the college in the town. On the suppression 
of these establishments in 1791, it became necessary to educate his 
three daughters with a view to gaining their living as teachers. But 
the eldest, Josephine, in view of the family difficulties, preferred to 

Avogadro 251 

take a situation in a linen-draper's in Paris, and there Gay-Lussac 
made her acquaintance. The young lady behind the counter he 
noticed to be reading attentively a small book which on enquiry 
turned out to be a treatise on chemistry. Naturally the interest in 
such a subject displayed by a girl of seventeen excited his curiosity, 


and something more, for his visits to the shop became more and 
more frequent and in the end the young lady accepted his offer of 
marriage. Gay-Lussac then placed her in a school in order to 
finish her interrupted education, and in no long time, namely in 
1808, she became his wife. The tender sympathy subsisting 
between Gay-Lussac and his wife during forty years controlled so 
completely their actions and even their habits as to extend even to 
their handwriting, and in the end it was impossible to distinguish 
the manuscript of a memoir copied by Madame from the original 
as it proceeded from the hand of her famous husband. 

The year 1808 was a memorable one for Gay-Lussac, for in it 
occurred not only his marriage but also his enunciation of the 
Law of the Combination of Gases by Volume, now generally known 

252 Avogadro 

as Gay-Lussacs Law. In a paper read to the Societe Philomatique 
on 31 December, Gay-Lussac announced that when gases react, 
their volumes bear a simple ratio to one another, and to the 
volume of the product if that is gaseous. He had observed that 
100 volumes of oxygen will combine with exactly 200 volumes of 
hydrogen and, suspecting that other gases might also combine 
in simple proportions by volume, he made several experiments 
on the combination of gaseous acids with ammonia. His surmise 
proved correct : 100 c.c. of ammonia require, for instance, looc.c. 
of hydrochloric acid gas ; and further work showed that the law 
was perfectly general. Thus, to form nitrous oxide, nitrogen 
and oxygen combine in the proportion by volume of 2 : i ; in 
nitric oxide the proportion is i : i ; and in nitrogen peroxide 
1:2. Two volumes of carbon monoxide will combine with one 
volume of oxygen to yield two volumes of carbon dioxide ; one 
volume of hydrogen combines with one volume of chlorine to 
form two volumes of hydrochloric acid gas ; and one volume of 
oxygen combines with two volumes of sulphur dioxide to form 
solid sulphur trioxide. 

The remarkable simplicity of these figures indicated that they 
possessed some deep significance, and the suggestion was made 
that, possibly, equal volumes of all gases contain equal numbers 
of atoms. Dalton had already considered and rejected this 
hypothesis in the New System of Chemical Philosophy, where he 
showed that it was not in accordance with experimental fact. 
'For*, he says, 'if equal measures of azotic and oxygenous gases 
[i.e. nitrogen and oxygen] were mixed, and could be instantly 
united chemically, they would form nearly two measures of 
nitrous gas [nitric oxide], having the same weight as the original 
measures ; but the number of ultimate particles could at most be 
one-half of that before the union. No two elastic fluids, probably, 
therefore, have the same number of particles, either in the same 
volume or the same weight/ 

Dalton was, indeed, inclined to believe that Gay-Lussac's 
experimental figures were inaccurate, and that the simplicity of 
his ratios was a deceptive one, due to this cause. He remarks 

Avogadro 253 

that he himself believes that 'gases do not unite in equal or exact 
measures in any one instance; when they appear to do so, it is 
owing to the inaccuracy of our experiments'. It is rather piquant 
to listen to Dalton chiding Gay-Lussac for experimental in- 
accuracy, when we remember that the great Englishman used to 
get a different result for the 'atomic weight' of carbon almost 
every time he determined it, while Gay-Lussac's manipulative 
precision has scarcely ever been surpassed. Yet we can under- 
stand the position : Dalton was firmly convinced of the truth of 
the atomic theory, but failed to see how it could be reconciled 
with Gay-Lussac's figures ; he was consequently led to question 
the accuracy of those figures. 

The way out of the impasse, which was also the way into the 
vast territory of nineteenth-century chemistry, was discovered 
by Avogadro. Accepting both Dalton 's theory and Gay- 
Lussac's facts, Avogadro perceived that the two could easily be 
brought into harmony if a distinction were made between the 
ultimate chemical particle of an element, the atom, and the 
ultimate physical particle of a substance, for which the name 
molecule is now employed. In the July number, of the year 181 1 , 
of Delametherie's Journal de Physique, de Chimie, d'Histoire 
naturelle et des Arts, he published his famous 'Essay on a Method 
of determining the Relative Masses of the Elementary Molecules 
of Substances'. Here is to be found the celebrated hypothesis 
that, like a pillar of fire, led chemists out of the wilderness 
into the promised land : 'Equal volumes of all gases at the same 
temperature and pressure contain equal numbers of molecules? 

Setting out from this hypothesis, [he continues] it will be seen that 
we have a means of determining very easily the relative masses of 
the molecules of compounds which can be obtained in the gaseous 
state, and the relative number of these molecules in compounds; 
for the ratios of the masses of the molecules are then the same as 
those of the densities of the different gases, at equal pressure and 
temperature, and the relative number of molecules in a compound 
is given directly by the ratio of the volumes of the gases that form 
it. For example, since the numbers 1-10359 and 0-07321 express 

254 Avogadro 

the densities of the two gases oxygen and hydrogen, taking that of 
atmospheric air as unity, and the ratio of these two numbers con- 
sequently represents the ratio between the masses of equal volumes 
of these two gases, it will also express, on the hypothesis suggested, 
the ratio of the masses of their molecules. Thus the mass of the 
molecule of oxygen will be about fifteen times that of the molecule 
of hydrogen, or, more exactly, 15*074 times. Similarly, the mass 
of the molecule of nitrogen will be to that of hydrogen as 0-96913 
is to 0-07321, that is, 13 to i, or more exactly 13-238 to i. On the 
other hand, since we know that the ratio of the volumes of hydrogen 
to oxygen in the formation of water is 2 to i , it follows that water 
results from the union of each molecule of oxygen with two mole- 
cules of hydrogen. Similarly, according to the proportions by 
volume established by M. Gay-Lussac in the elements of ammonia, 
oxide of nitrogen [nitrous oxide, N 2 O], nitrous gas [nitric oxide, 
NO] and nitric acid [nitrogen peroxide, NO 2 ], ammonia will 
result from the union of one molecule of nitrogen with three of 
hydrogen, oxide of nitrogen from one molecule of oxygen with two 
of nitrogen, nitrous gas from one molecule of nitrogen with one of 
oxygen, and nitric acid from one of nitrogen with two of oxygen. 

In the light of this hypothesis, let us re-examine the case of 
nitric oxide, which Dalton found such a stumbling-block. It is 
an experimental fact that if one volume of nitrogen and one 
volume of oxygen are caused to enter into chemical combination, 
the product is two volumes of nitric oxide. According to 
Avogadro, therefore, one molecule of nitrogen will combine with 
one molecule of oxygen to form two molecules of nitric oxide. 
Each molecule of nitrogen, and of oxygen, must thus have been 
halved, and consequently must consist of an even number of 
atoms, at least two. It was Dalton 's failure to realize the 
possibility that the smallest elementary particles normally exist- 
ing in the free state might consist of a congeries of chemical atoms 
of that element, and not of single atoms, that effectively blocked 
his progress. "Thou knowest that no man can split an atom* was 
such an idie fixe with him that it excluded the visualization of 
elementary particles of atomic dimensions that yet consisted 
of more than one atom. Avogadro, on the other hand, did not 

Avogadro 255 

shrink from the only conclusion to be drawn from the experi- 
mental facts, and thus made the vital distinction between an 
atom which retained the Daltonian indivisibility and a mole- 
cule, which might or might not be divisible, according as to 
whether it consisted of more than one atom or of a single atom. 


, ^^^ 


With this efficient tool to help them, chemists might have 
made rapid progress in the determination of atomic weights and 
in the investigation of the structure of molecules. Thus, when 
one volume of hydrogen enters into combination in such a way 
as to yield a gaseous product, or one which can be volatilized, it 
often yields two volumes of the product but never more. The 
conclusion is that the molecule of hydrogen contains two, and 
not more than two, atoms. Similarly, one volume of oxygen will 
often yield two, but not more than two, volumes of a gaseous 
compound, and the conclusion to be drawn is consequently that 
the molecule of oxygen, like that of hydrogen, is diatomic. Now, 

256 Avogadro 

two volumes of hydrogen will combine with one volume of 
oxygen to form two volumes of steam. Hence, by Avogadro 's 
hypothesis, each molecule of steam must consist of one molecule 
of hydrogen and half a molecule of oxygen: in other words, its 
constitution must be H 2 O, and not IIO as Dalton had supposed. 
This in turn requires the doubling of Dalton 's number 8 for the 
atomic weight of oxygen : and so on. 

After the publication of Avogadro's hypothesis, indeed, 
chemists had it within their power to settle innumerable 
problems that, in point of fact, were not settled until nearly half 
a century later. This unexpected delay was due to several 
reasons. In the first place, chemists had not thoroughly assimi- 
lated the atomic theory, and although they accepted it in prin- 
ciple they seem often to have regarded it more as a picturesque 
flight of the philosophic imagination than as a solid, practical 
scientific theory. Secondly, Dalton never lent his weighty 
support to Avogadro 's hypothesis, and on matters connected 
with atoms his verdict was unchallenged. Thirdly, experimental 
methods had improved so much that men had their time fully 
occupied with practical work : new elements and new compounds 
were being discovered with amazing rapidity, and a minimum 
of theory sufficed. Lastly, chemists appear to have shared with 
Dalton the difficulty of conceiving a distinction between the 
atom and the molecule, and thus overlooked the fundamental 
importance of Avogadro 's suggestion. Perhaps, too, the political 
state of Italy at that time, when Metternich could say * Italy is 
a geographical expression', may have contributed to the neglect 
that Avogadro suffered. 

Avogadro himself returned to the attack again and again, but 
with so little success that his hypothesis was not mentioned in 
his obituary notice in the Nuovo Cimento of 1856, in Kekule's 
great text-book of organic chemistry (1859-61), or even in 
Kopp's History of Chemistry (1843-7). It was not until 1858, 
two years after his death, that Avogadro at length triumphed. 
In the half century that had elapsed, confusion over atomic 
weights and molecular formulae had steadily grown, and 

Modern Chemistry Established 257 

there seemed little possibility of bringing the chaos to order. 
Fortunately, however, Avogadro's fellow-countryman, Stanislao 
Cannizzaro (1826-1910) had become thoroughly persuaded of 
the basic importance of the then almost forgotten hypothesis, 
and in a masterly pamphlet, entitled A Summary of a Course of 
Chemical Philosophy, he so lucidly and convincingly explained 
the manner in which it smoothed away the difficulties of con- 
temporary chemical theory that chemists were at last converted. 
Only a few years later, Avogadro was universally acclaimed as 
one of the founders of theoretical chemistry ; atomic weights had 
been definitely fixed; the structure of molecules could be in- 
vestigated with confidence ; and chemistry strode forward shod 
with seven-league boots. 

Avogadro's hypothesis [wrote Lothar Meyer] has had a great in- 
fluence particularly upon the development of chemical theories. 
It was not until after it had been generally adopted and its con- 
sequences studied, that the most important laws governing the 
combinations of atoms with one another were discovered. From 
Avogadro's laws dates the beginning of a general theory of 
chemistry, a theory which explains the atomic constitution and the 
major part of the properties of compound bodies. . . . The gradual 
development of this theory has become the base of a science of the 
equilibrium of atoms; it marks a new period in the history of 
chemical statics. 

53. Modern Chemistry Established 

OUR story proper now ends, for after Lavoisier had replaced 
phlogiston by o'xygen; Dalton had established the atomic theory ; 
Berzelius had shown how it could be universally applied; and 
Avogadro had crowned all with his brilliant hypothesis, chemistry 
was already advancing on her present lines. The 'makers of 
chemistry' those who fashioned it into the science as we know 
it had accomplished their work, and a chemist of 1831 would 
feel more at home with the chemistry of 1931 than with that of 
1781 . True, he would be at first bewildered by the multitudes of 
new compounds, new elements, new reactions, new applications, 
but he would find the oxygen theory still reigning, the name of 

2613-4 c 

258 The Electrochemical or Dualistic Theory 

Dalton in present reverence, and Avogadro's hypothesis in 
universal currency. After the first amazement had evaporated, 
he would realize that the basic theories of modern chemistry 
were the basic theories of his own day ; he would find expansion, 
extension, modification, but no such revolution as that which was 
witnessed by the closing years of the eighteenth century. The 
world has produced chemists of scintillating genius in the nine- 
teenth and twentieth centuries, but their work, marvellous 
though it be, is but a working out of the principles laid down by 
Lavoisier, Dalton and Avogadro. 

Yet the reader who has travelled thus far may wish to com- 
plete his journey, and to take at least a passing glance at the 
development of chemistry in the last hundred years. The short 
survey that follows may serve to whet his appetite for more 
detailed study, and to throw into bolder relief the great work 
accomplished by those makers of a science 'which reveals, 
creates, and indefinitely renews the dominion of human in- 
telligence and labour'. 

54. The Electrochemical or Dualistic Theory 

THE rapid extension of chemical knowledge in the early years 
of the nineteenth century gradually led to a ramification of 
the subject into several distinct branches a process that has 
become intensified with the passage of time. The first great 
division was effected when the chemistry of mineral products, or 
inorganic chemistry, was distinguished from that of animal and 
vegetable products, or organic chemistry. The latter, as we shall 
see, eventually resolved itself into the chemistry of the com- 
pounds of carbon, while the former is concerned with all other 
elements and their compounds. The distinction between in- 
organic and organic chemistry is, at bottom, a matter of con- 
venience of study only ; the same principles reign in both pro- 
vinces, and the general theory of chemistry holds sway over 
each, as the Pharaoh was King of both Upper and Lower Egypt. 
For the first half of the century, inorganic chemistry was 
chiefly concerned with the determination of the combining 

The Electrochemical or Dualistic Theory 261 

were passed through them. Two such bodies were caustic soda 
and caustic potash. It is true that Lavoisier had expressed the 
opinion that they were metallic compounds containing oxygen, 
but the suggestion had never been substantiated and remained 
a mere supposition, though an attractive one. In 1807, however, 


Davy subjected fused caustic soda and potash to the action of 
a strong electric current, and had the intense satisfaction of 
observing each of them to be split up : the soda into oxygen, 
hydrogen and the soft metal now known as sodium , and the 
potash into the same two gases and the similar metal potassium. 
These astonishing phenomena, together with his own observa- 
tions, led Berzelius in 1819 to publish his celebrated 'electro- 
chemical' theory. Like Davy, he assumed that chemical and 
electrical attraction are essentially identical, but he went con- 
siderably, farther than Davy in the elaboration of detail and in 
the correlation of theory with experimental fact. According to 
Berzelius, all atoms are charged with electricity and show a 
polarity, i.e. they have positive and negative poles. The two 
poles are, however, not equal in strength; in some cases the 
positive pole predominates and in others the negative. By reason 
of this 'unipolarity' of their atoms, elements are either electro- 
negative or electropositive, appearing at the anode or cathode 

262 The Electrochemical or Dualistic Theory 

respectively in electrolysis. The degree of chemical affinity of 
a substance depends upon its intensity of polarization, which 
itself varies with the temperature. Chemical combination con- 
sists in the neutralization of electricity between oppositely 
charged poles, and since each atom has both a positive and 
a negative pole it is quite possible for two electronegative 
elements to combine with one another, or two electropositive 
ones, though in general, of course, combination occurs most 
easily between elements of opposite electric character. 

When an electropositive element combines with an electro- 
negative one, the particles of the compound so formed may still 
show a predominating residual polarity. Thus when copper (+) 
combines with oxygen ( ), the copper oxide particles are still 
slightly electropositive, while sulphur trioxide in which the 
positive pole of the sulphur neutralizes part of the negative 
electricity in the dominant pole of the oxygen is electronegative. 
Copper oxide can therefore combine with sulphur trioxide to 
form copper sulphate; but even this compound shows slight 
polarity and is therefore able to combine with other sub- 
stances to form more complex bodies, and so on. 'If the con- 
jectures I have just explained give a just idea of the relation 
between substances and electricity/ said Berzelius, 'it follows 
that what we call chemical affinity, in all its varieties, is nothing 
else but the effect of the electric polarity of the particles, and 
that electricity is the prime cause of all chemical action. . . . 
Every chemical combination follows solely from two opposing 
forces, positive and negative electricity, and similarly every 
compound is formed of two constituent parts united by the 
effect of their electrochemical reaction, since no third force 
exists. Thence it follows that every compound body, whatever 
the number of its prime constituents, may be divided into two 
parts, of which one is electropositive and the other electro- 
negative. Thus, for example, sodium sulphate is not made up 
[immediately] of sulphur, oxygen, and sodium, but of sulphuric 
acid [SO 3 ] and soda [NaO], each of which may itself be split 
up again into two elements, one positive and the other negative.' 

The Classification of the Elements 263 

Berzelius would, in fact, have written the formula for sodium 
sulphate (using our notation) as Na 2 O . SO 3 rather than as 
Na 2 SO 4 , to emphasize the view just expressed. 

The electrochemical or 'dualistic' theory of the formation and 
structure of compounds received widespread support, and led 
directly to great progress in the investigation of molecular archi- 
tecture. It finally encountered certain obstacles that rendered 
it untenable in the form which Berzelius and his followers gave 
it, but it was a remarkably penetrating conception, and its main 
doctrine the intimate connexion between chemical and elec- 
trical affinity has been revived in recent years and is now 
universally held. 

55. The Classification of the Elements 

THE framework of inorganic chemistry was materially strength- 
ened and enlarged during the nineteenth century by the slow 
elaboration of a consistent scheme of classifying the elements. 
The possibility of this scheme is due to Lavoisier, who first 
drove home the definition of an element suggested by Boyle, 
and himself drew up a ' Table of Simple Substances' in which 
the elements known at that time were systematically arranged 
in four groups, viz. 

i. Simple Substances belonging to all the [three} kingdoms of 
nature, which may be considered as the elements of bodies. 


Caloric (heat) 


Azote (nitrogen) 


ii. Oxydable and Acidifiable simple Substances not Metallic. 

'Miiriiim' 1 still unknown, but the existence of 
Munum inferred Actua n y the 

Phosphorus 'Fluorum' > muriates contained chlorine, the 

Carbon 'BoraCUm' fl uorates fluorine, and the borate* 


264 The Classification of the Elements 

iii. Oxydable and Acidifiable simple Metallic Bodies. 

Antimony Mercury 

Arsenic Molybdenum 

Bismuth Nickel 

Cobalt Platinum 

Copper Silver 

Gold Tin 

Iron Tungsten 

Lead Zinc 

iv. Salifiable simple Earthy Substances. 

at that time still regarded as elements, 

Magnesia though Lavoisier foresaw that they 

Baryta ^ 'must soon cease to be considered as 

Argill (earth of alum) 

simple bodies', and that they were per- 

O . r haps metallic oxides. 

Silica j F 

More detailed classifications of the elements on the basis of 
similarities in chemical properties were worked out by Dumas, 
Odling and other chemists, and the existence of 'families' of 
elements was recognized. Thus, fluorine, chlorine, bromine and 
iodine form a natural family, as do oxygen, sulphur, selenium 
and tellurium, and nitrogen, phosphorus, arsenic, antimony and 
bismuth. Such schemes, however, had no fundamental unifying 
principle, and were consequently in a perpetual state of flux. 
Elements have numberless properties, and different selections of 
the latter inevitably led to different classifications. 

The problem was placed upon a new footing by the work of 
Dobereiner (1829) and Pettenkofer (1850). Dobereiner observed 
that many chemically related elements formed well-marked 
groups of three (Dobereiner^ s Triads) , the atomic weight of the 
middle member of each group being approximately the mean of 
the atomic weights of the other two. Thus the atomic weight of 
bromine (80) is roughly the mean of 35-5 and 127, the atomic 
weights of chlorine and iodine respectively. Calcium (40), 

The Classification of the Elements 265 

strontium (87), and barium (137) form another such group. 
Pettenkofer showed that certain arithmetical relationships 
existed between the atomic weights of chemically similar 


elements. Thus, the atomic weights of lithium (7), sodium (23), 
and potassium (39), can all be represented by the formula 
7+2/z8, where n = o, i, and 2 in the first, second and third cases 
respectively. The atomic weights of other groups of elements 
lent themselves to the same kind of mathematical expression, 
and it was generally felt that such numerical relationships could 
scarcely be due to chance. 

Greater progress was not to be expected at the time, owing to 
the uncertainty as to the atomic weights of many elements . How- 
ever, after Cannizzaro, in 1858, had drawn the attention of 
chemists to the great value of Avogadro's Hypothesis in deciding 

266 The Classification of the Elements 

between rival values for atomic weights, and the latter were at 
last definitely fixed, further interesting relationships became 
obvious almost at once. An important advance was made by the 
English chemist Newlands in several short papers published 
between 1863 and 1866. Newlands pointed out that when the 
elements were arranged in order of their atomic weights, as 


determined in the light of Avogadro's Hypothesis, the eighth 
element resembled the first, fifteenth, &c., the ninth resembled 
the second, sixteenth, &c., and so on. Each element, in fact, 
more or less closely resembled the elements that were seven, or 
some multiple of seven, places before it or after it. One of 
Newlands 's tables, published in the Chemical News of 1865 is as 
follows : 




No. \ 


No. \ 



H i , F 8 

Cl 15 

Co Ni 

22 | 






42 Pt Ir 50 

Li 2 

Na 9 ; K 16 








44 Tl 53 

G 3 

Mg 10 Ca 17 









Pb 54 

Bo 4 

Al ii 

Cr 19 








46 Th 56 

C 5 

Si 12 

Ti 18 








47 Hg 52 

N 6 

P 13 

Mn 20 









Bi 55 


S 14 Fe 21 


28 , 







Os 51 

He says that, making a 'few slight transpositions', it will be 
seen that elements belonging to the same group usually appear 
on the same horizontal line. ' It will also be seen that the numbers 
of analogous elements generally differ either by 7 or by some 
multiple of 7; in other words, members of the same group 
stand to each other in the same relation as the extremities of one 
or more octaves in music. Thus, in the nitrogen group, between 
nitrogen and phosphorus there are 7 elements; between 










Fig. 88 

268 The Classification of the Elements 

phosphorus and arsenic, 14; between arsenic and antimony, 14; 
and lastly, between antimony and bismuth, 14 also. This pecu- 
liar relationship I propose provisionally to term the "Law of 
Octaves/ 1 ' 

When Newlands expounded his Law of Octaves before the 
Chemical Society on i March 1866, it did not meet with an 
enthusiastic reception. One member of the audience inquired, 
pertinently, what provision the table made for elements still un- 
discovered ; and a second, impertinently, whether Mr. Newlands 
had ever tried arranging the elements in the order of their 
initial letters ! Newlands was seriously discouraged by the good- 
humoured, if tactless, derision his suggestion suffered, and after 
brief replies to his critics pursued the matter no farther. 

The 'simple but important' idea, as Wurtz described it, of 
arranging the elements in order of increasing value of their 
atomic weights had, however, already occurred independently 
to two other chemists the German Lothar Meyer and the 
Russian Mendeleeff. Like Newlands, Meyer and Mendeleeff 
were struck by the periodicity of properties that become 
apparent when such an arrangement was drawn up, but both 
went much farther than Newlands in their treatment of the 
subject. In its final form, the scheme elaborated by Mendeleeff 
incorporated nearly the whole of Lothar Meyer's results, so that, 
having given Germany her meed of honour, we may consider 
the 'Periodic Law' in its Russian garb only. 

In 1866 Mendeleeff a forceful personality of the genuine 
Slav type was made Professor of Chemistry in the University 
of St. Petersburg (bolshevike Leningrad). Three years later, at 
the age of 35, he published his epoch-making paper on the 
classification of the elements, in which he described the arrange- 
ment that has since become celebrated as the Periodic System. 
Like Newlands (of whose work it appears he was in ignorance) 
he arranged the elements in order of their atomic weights, 
starting from the lowest, and called attention to the fact that 
chemically similar elements recurred at approximately equal 
intervals. This, of course, had been already observed by New- 

The Classification of the Elements 269 

lands, but Mendeleeff had an incomparably greater knowledge 
of general chemistry, and was able to overcome many of the 
difficulties that had prejudiced chemists against the original 'law 
of octaves'. 

The conclusions at which Mendeleeff arrived are as follows : 


1. The elements, if arranged according to their atomic 
weights, exhibit an evident periodicity of properties. 

2. Elements that are similar as regards their chemical pro- 
perties have atomic weights which are either of nearly the same 
value (e.g. platinum, iridium, osmium), or which increase 
regularly (e.g. potassium, rubidium, caesium). 

3. The arrangement of the elements, or of groups of 
elements, in the order of their atomic weights corresponds to 
their valencies as well as, to some extent, to their distinctive 
chemical properties as is apparent among other series in that 

270 The Classification of the Elements 

of lithium, beryllium (glucinum), barium, carbon, nitrogen, 
oxygen, and iron. 

4. The elements which are the most widely diffused have 
small atomic weights. 

5. The magnitude of the atomic weight determines the character 
of the element, just as the magnitude of the molecule determines 
the character of a compound body. 

6. We must expect the discovery of many yet unknown 
elements, for example, elements analogous to aluminium and 
silicon, whose atomic weight would be between 65 and 75. 

7. The atomic weight of an element may sometimes be 
amended by a knowledge of those of the contiguous elements. 

8. Certain characteristic properties of the elements can be 
foretold from their atomic weights. 

Mendeleeff's brilliant scheme, springing fully armed from the 
head of its creator, speedily conquered the chemical world. One 
of its most compelling features was the confident boldness with 
which it made predictions, and the breath-taking audacity it 
showed in rejecting as erroneous atomic weights that did not fit 
into its pigeon-holes. Tellurium has an atomic weight of 127-5, 
while that of iodine is 127 ; the positions of these two elements in 
the Table (p. 271) should therefore be reversed. On the contrary, 
said Mendeleeff; iodine must clearly be classified with fluorine, 
chlorine and bromine therefore the atomic weight of tellurium 
must have been determined incorrectly and should be less than 
that of iodine, probably 125. Again, arsenic has undoubted 
affinities with nitrogen, phosphorus, antimony and bismuth, but 
to put it in this group leaves two blank spaces in Groups III and 
IV. Very well, remarks the undaunted Russian there must be 
two elements not yet discovered that will, at some future time, 
satisfactorily fill these vacant spaces. 

It was this spirit of fearless prediction that fascinated con- 
temporary chemists, even more than the patent success of the 
system in grouping together elements which are chemically 
similar. Mendeleeff nailed his colours to the mast, and showed 
the firm faith that burned within him by predicting in detail the 

oo ^ 


r? O M M 


^ rj ^ ^r* ^ 3 


^CJ ^ ^ < 


(^ ^ ^ Q OO 


^^ 2^ ?n 

[T < pr^ Q 


iO O t > * 


^ 00 CJ 

o o w 8 *"* 


2^ c *"* 


ta 1 



N OO iO 
CO 1> M 

C/3 " 



M F-* "^l" 



^O Ir > O> t" 1 QQ 



oil ^ 



M o N OC 
co l> c* C 




PL, ^ M c 

2- < $ S 


pj *O ^Q ^ 


/C > ^ H 





c/5 ^ r 



Co X 

CO O </} 2" *2 ^ 


*" -M Ui <U C3 


a h N u j 






S* Ho 




~! -S oo oo E 

<C rf OO CO |> ~ 

^ ^ ^ 00 

4_> "J? *-" 

PQ K^ Q W 


rf to N C 


^) ^ M C 



PQ U c/5 

ro co OO C 


w N ^0 O C 


ffi ^ 3 Sj 



r^ g ^ ? 

3 & e u 


M N co -^ o ^o r^oo c^ 2 M 


272 The Classification of the Elements 

properties that the elements of atomic weight 44, 68 and 72, 
and their compounds, would be found to possess when they 
were discovered. The element of atomic weight 72, he foretold, 
would have a specific gravity of 5-5. Its oxide would be of the 
type MO 2 and possess a specific gravity of 4-7. Its chloride, 
MC1 4 , would be a liquid of specific gravity i -9 and would boil at 
a temperature just below iooC. It would form a derivative 
M(C 2 H 5 ) 4 , and this would be a liquid boiling at i6oC. and 
possessing a specific gravity of 0-96. 

In 1887, Winckler discovered a metal of atomic weight 72-5. 
He called it germanium (Ge). Its specific gravity was 5-5. It 
formed an oxide GeO 2 , of specific gravity 4-7 ; a chloride GeCl 4 , 
which was a liquid boiling at 86 C. and possessing a specific 
gravity of 1-9; and a derivative Ge(C 2 II 5 ) 4 , which boiled at 160 
C. and had a specific gravity rather less than i. Small wonder 
that Mendeleeff confessed to feelings of pride and gratification, 
still further swollen by the discovery of gallium and scandium, 
which admirably fitted the blank spaces between zinc and 
germanium, and calcium and titanium, respectively. 

The Periodic System proved useful in another direction, 
namely, the correction of the atomic weights of certain elements. 
It had, for instance, been shown that the equivalent of indium 
(In) is 38, and the atomic weight was believed to be twice this, 
i.e. 76. There was, however, no place in the system for an 
element of atomic weight 76 having the properties of indium, 
and Mendeleeff therefore suggested that the valency of indium 
was 3 and the atomic weight 38 x 3, or 114. This would make 
indium fall into the (at that time) vacant space in Group III 
between cadmium and tin. Further research on indium com- 
pounds proved that Mendeleeff was right. The atomic weights of 
beryllium, uranium and Jjold were similarly corrected, but 
MendeleefPs prediction that tellurium must have an atomic 
weight less than that of iodine was definitely falsified. The dis- 
covery of the rare gases (helium, neon, argon, krypton and 
xenon) in the last decade of the nineteenth century provided the 
periodic system with another anomaly of the same kind. While 

The Rise of Organic Chemistry 273 

there was no space for these gases in the table as Mendeleeff 
constructed it, the difficulty was immediately overcome by con- 
structing a new group Group O before Group I. But to get 
argon (atomic weight 40) into this group meant that it had to 
come before potassium (atomic weight 39) ; and in neither case 
was there any doubt that the atomic weight had been determined 

These anomalies were not sufficient in number to detract from 
the grandeur of the Periodic Classification, but they afforded 
matter for speculation. No solution of the enigma could be 
offered, however, until early in the present century, when it was 
shown that the atomic weight of an element is a less fundamental 
property than had been supposed. t If a more fundamental 
characteristic, namely the atomic number of the element (p. 297) 
is adopted as the basis of the classification, it is found that argon 
and potassium, tellurium and iodine fall naturally into their 
appropriate groups. Thus, although the atomic weight of argon 
is greater than that of potassium, its atomic number is less ; and 
the same is true of tellurium (atomic number 52) and iodine (53). 

The essential significance of the Periodic System was to show 
that the chemical elements are not 'mere fragmentary, incidental 
facts in nature', but that they form successive units in the 
sublime harmony of the universe. 

56. The Rise of Organic Chemistry 

IN the city of Cologne, some hundreds of years ago, two officers 
of the Holy Inquisition wrote their terrible book Malleus 
Maleficarum, or 'Hammer of Witches', in order to try to free 
mankind from the supposed scourge of witchcraft. To-day, in a 
delightful suburb of the city, one may see the house in which lived 
Adolf von Baeyer, who did more than any other man to free the 
world from the scourge of pain : for von Baeyer was the discoverer 
of aspirin. Aspirin is a compound of carbon with hydrogen and 
oxygen, and in this respect it is similar to ether, alcohol, sugar, 
starch, acetic acid, mutton-fat and thousands of other sub- 
stances. Petrol, fire-damp, lubricating-oil, paraffin, vaseline v 

2613-4 T 

274 The Rise of Organic Chemistry 

benzene, acetylene and naphthalene are likewise compounds of 
carbon, but in these examples the only other element present is 
hydrogen. With hydrogen and nitrogen, carbon forms prussic 
acid and hundreds of dyes ; with hydrogen, oxygen and nitrogen 
it forms most of the modern high explosives; with hydrogen, 
oxygen, nitrogen and phosphorus it forms the basis of living 
matter or protoplasm. Carbon is, indeed, unique among the 
elements in its power of entering into innumerable combinations, 
and for this reason the study of carbon compounds has grown 
into a distinct branch of chemistry a branch which is at once 
the most systematic and, as many feel, the most fascinating. 

The earliest known carbon compounds were all derived, 
either directly or indirectly, from living or dead organisms 
plants and animals and in this circumstance lies the origin of 
the term 'organic' chemistry. As a distinct branch of the science, 
organic chemistry is little more than a century old. Various 
carbon compounds had, it is true, been known for hundreds 
perhaps thousands of years, but they had not been so fully or 
so satisfactorily studied from a chemical point of view as the 
metals, metallic compounds, sulphur and other acids, and 
mineral or 'inorganic' substances in general. Thus the nations 
of the ancient world prepared wine, beer and mead, of which the 
intoxicating principle is the organic compound alcohol '; vinegar, 
containing acetic acid, was obtained by the souring of wine; 
indigo and certain other dyes were employed; and starch, sugar 
and fats formed part of man's daily food. Organic chemistry 
proper, however, may be said to have begun in the hands of the 
great Swedish chemist Scheele (1742-86), who was the first to 
prepare pure specimens of such typical organic compounds as 
glycerine, prussic acid, citric acid and oxalic acid. 

Lavoisier was among the founders of organic analysis. He 
showed that 'organic' compounds usually contain carbon, 
hydrogen and oxygen, and less often nitrogen, sulphur and 
phosphorus. Further improvements in the methods of analysis 
were made by Berzelius, and it was at length realized that the 
essential element in all organic compounds is carbon. One of 

The Rise of Organic Chemistry 275 

the first chemists to state this important fact was Gmelin, who in 
his Handbook of Chemistry (1848) claimed that organic chemistry 
should be'definitely regarded as the chemistry of the compounds 
of carbon. 

For many years, it was believed that the formation of organic 
compounds in plants and animals was occasioned by a mysterious 
vis vitalis or Vital force*, and that it was impossible to synthesize 
them, or build them up from their elements, in the laboratory. 
Even though many naturally occurring substances, such as 
formic acid and oxalic acid, had been prepared artificially by 
chemists, the starting-point in each of these preparations had 
been other organic substances ; no one had succeeded in making 
any organic compound from 'inorganic' material. The solution 
of this problem was, in fact, very slow in coming, and disbelief 
in the vis vitalis was not shattered at a blow, but died a lingering 
death throughout a period of many years, during which a more 
adequate study of organic substances had brought about a fuller 
appreciation of the fact that they were amenable to the ordinary 
chemical laws. 

The term 'organic' chemistry, though it has now lost its 
original significance, is less cumbersome than 'the chemistry of 
the compounds of carbon', and is thus still used, in spite of the 
fact that the majority of organic compounds at present known 
have been built up in laboratories rather than by plants or 

The possibility of vast and rapid progress was secured to 
organic chemists by the elaboration, at the hands of Justus von 
Liebig (1803-73), of a simple but reliable method of quantitative 
analysis. The method adopted by Berzelius was capable of yield- 
ing excellent results, but it was very slow; he spent eighteen 
months, for instance, in analysing seven compounds. Liebig's 
method was such an improvement that seventy-two analyses 
were completed in three months, without a single failure. In 
a modified form, Liebig's procedure is still employed, and its 
ease and simplicity rendered possible the accurate analysis of 
innumerable substances in a comparatively short time. With 


276 The Rise of Organic Chemistry 

the data thus available, theoretical speculations could be made, 
and Liebig himself in collaboration with his life-long friend 
Wohler established the extraordinarily fruitful Radical Theory. 
The germ of this theory can be traced back to Lavoisier, who 
regarded organic compounds as 'oxides of compound radicals', 
the words compound radical here signifying a group of atoms one 
at least of which is carbon. Adopting and amplifying Lavoisier's 
conception, Liebig and Wohler defined a compound radical as 
a group of atoms which (a) is present as such in a series of com- 
pounds, (b) can be replaced as a whole in these compounds, and 
(c) can enter into combination as a whole. This theory can 
readily be understood by reference to the particular example 
first chosen by Liebig and Wohler, namely, the benzoyl radical. 
In modern notation, this radical is represented by the formula 
C 6 H 5 . CO , and they proved that this group of atoms is present 
in the following compounds : 

Benzoicacid . . C 6 H 5 . CO . OH 

Oil of bitter almonds . C 6 II 5 . CO . H 

Benzoyl chloride . C 6 H 5 . CO . Cl 

Benzoyl bromide . C 6 H 5 . CO . Br 

Benzoyl iodide . . C 6 H 5 . CO . I 

Benzoyl cyanide . . C 6 H 5 . CO . CN 

Benzoyl sulphide . (C 6 H 5 . CO) 2 S 

Benzamide . . C 6 II 5 . CO . NH 2 . 

The publication of this classical memoir created great excite- 
ment. Berzelius himself wrote: 'The results you have drawn 
from the investigations of the oil of bitter almonds are certainly 
the most important that have hitherto been obtained in the 
domain of vegetable chemistry . . . one may indeed regard them 
as the beginning of a new day' ; while Pelouze wrote to Liebig : 
'Your experiments are the sole topic of the chemical world in 
Paris. So come along, and bring M. Wohler, come and receive 
the tribute of admiration that is due to you.' 

Following up this initial success with many others, Liebig at 
last felt justified in describing organic chemistry as the chemistry 

The Rise of Organic Chemistry 277 

of compound radicals, and the discovery of other radicals, such as 
those of cinnamic and salicylic acids, and especially the cacodyl 
radical, As(CH 3 ) 2 , lent emphasis to the importance of these 
various groups of atoms as the structural units of organic mole- 
cules. At the present time, by a mere inspection of its structural 


formula, a chemist can describe with confidence the chief pro- 
perties of an organic compound he may never have seen or even 
heard of simply because he knows the properties of the radicals 
of which the molecule of the substance is composed. 

Meanwhile, another fertile theory had been developed: the 
theory of substitution or theory of types. The French chemist 
Dumas had found that part or all of the hydrogen in certain 
organic compounds could be replaced by chlorine without any 
fundamental change in the structure of the molecule ; such com- 
pounds he called types. At first, there was a sharp conflict 

278 The J^ise of Organic Chemistry 

between Liebig and his followers and the protagonists of the 
theory of substitution, for it was hard to believe that the replace- 
ment of an atom of the electropositive element hydrogen by an 
atom of the electronegative element chlorine could have so 
little effect upon chemical properties as the theory of Dumas 
implied. The facts, however, were afterwards recognized to be 
incontrovertible, and a reconciliation between the two schools 
was effected by the work of the Frenchmen Laurent and 
Gerhardt (1853). Into the details of their scheme it is not 
possible for us to inquire, but it led to the elaboration of a com- 
prehensive theory of molecular architecture by Frankland ( 1 825- 
-99) and Kekule (1829-96). 

In spite of the clarity of Laurent and Gerhardt 's views, a full 
understanding of the structure of organic molecules was im- 
possible until Cannizzaro, in 1858, had demonstrated the im- 
portance of Avogadro's Hypothesis in deciding the true values of 
atomic and molecular weights. Up to that time, some chemists 
had taken the atomic weight of carbon to be six and others twelve, 
so that no little confusion reigned. Those who adopted the 
former number wrote twice as many carbon atoms in the formula 
of an organic compound as the latter, with the result that any 
decision on the way in which the atoms were arranged in the 
molecule was merely provisional. 

As soon as Cannizzaro 's views were generally accepted, how- 
ever, these exasperating difficulties vanished, and it was univer- 
sally agreed that the atomic weight of carbon is twelve. This 
agreement in its turn led to unanimity on the number of carbon 
atoms in the molecule of any particular organic compound, and 
the way to a full elucidation of molecular architecture was open. 
A phenomenon that early attracted the attention of chemists 
was the existence of substances whose molecules consisted of the 
same numbers of the same atoms, though the substances them- 
selves were different from one another in chemical and physical 
properties. In 1828 Liebig's collaborator Wohler obtained urea 
from ammonium cyanate by merely dissolving the latter in 
water and evaporating the solution. Analysis showed that each 

The Rise of Organic Chemistry 279 

compound had the formula CON 2 H 4 , so that to account for the 
differences between them chemists had to assume that the atoms 
were arranged in the molecule of urea in a different manner from 
that in the molecule of ammonium cyanate. Other examples of 
the same phenomenon were quickly forthcoming, and Berzelius 

Fig. 91. KEKULE 

coined the word isomerism to denote it (from the Greek, meaning 
'of equal parts'). 

The existence of isomerism rendered ordinary formulae in- 
sufficient to characterize organic compounds. It is not enough 
to know how many atoms of each particular element are present 
in the molecule of a compound of carbon ; to understand the 
reactions of the substance and to give it an unequivocal formula, 
the mode in which those atoms are grouped within the molecule 
must be ascertained and expressed. That such a formidable 
problem was triumphantly solved is due very largely to the work 

280 The Rise of Organic Chemistry 

of two chemists, Sir Edward Frankland (1825-99) an ^ Friedrich 
August Kekulc (1829-96). 

In a memorable paper published in the Philosophical Transac- 
tions in 1852, Frankland set out his views on the 'combining 
power' or saturation capacity of atoms, and thus laid the 
foundation of the theory of valency. By the valency of an atom 
is meant the number of units into which the combining capacity 
of that atom may be divided ; thus the atom of oxygen will in 
general combine with either one or two atoms of other elements, 
but not more, while the atom of hydrogen will combine with one 
atom of other elements, but not more : the valency of oxygen is 
therefore considered to be two and that of hydrogen one. Frank- 
land was led to this conception by a systematic survey of the 
formulae of inorganic compounds. 'When the formulae of in- 
organic chemical compounds are considered,' he says, 'even 
a superficial observer is struck with the general symmetry of 
their construction; the compounds of nitrogen, phosphorus, 
antimony and arsenic especially exhibit the tendency of these 
elements to form compounds containing three or five atoms of 
other elements, and it is in these proportions that their affinities 
are best satisfied. . . . Without offering any hypothesis regarding 
the cause of this symmetrical grouping of atoms, it is sufficiently 
evident, from the examples just given, that such a tendency or 
law prevails, and that no matter what the character of the uniting 
atoms may be, the combining power of the attracting element, 
if I may be allowed the term, is always satisfied by the same 
number of these atoms/ 

Kekule greatly improved and extended Frankland's theory, 
and in his celebrated Textbook of Organic Chemistry (1859) he 
insisted upon the facts (a) that carbon is uniformly quadrivalent 
in organic compounds, and (b) that carbon atoms have the re- 
markable power, unshared except in a very limited degree by 
those of other elements, of linking up together to form chains. 1 

1 Similar views were published almost simultaneously by a young Scottish 
chemist, A. S. Couper, who was unfortunately unable to elaborate his thesis 
on account of ill health. 

The Rise of Organic Chemistry 281 

To illustrate the valency of atoms, Kekule used curious dia- 
grams (' Kekule 's sausages') of which the following are examples : 

This unwieldly notation was very short-lived, for in 1865 
Crum Brown introduced the modern system, in which each 
Valency' or unit of combining power is indicated by a line. 
Thus Kekule 's sausages shown above were represented by Crum 
Brown as 

-O- and -C- 


respectively: a much more elegant, and equally intelligible, 

After the establishment of the theory of valency, and its 
practical expression in such a simple form, insight into many 
puzzling problems of organic chemistry was quickly obtained. 
The existence of isomeric substances was afforded a mechanical or 
spatial explanation, and this explanation could be conveyed in a 
clear and concise manner in the 'structural' formulae of the com- 
pounds. There are, for instance, two compounds known of the 
formula C 2 H 6 O, i.e. the molecules of each of them consist of two 
atoms of carbon, six of hydrogen, and one of oxygen. Assuming, 
with Kekule, that carbon is quadrivalent, oxygen bivalent, and 
hydrogen univalent, we can arrange these atoms in two ways, viz. 
H H H H 

(i) H-C-C-O-H and (ii) H-C-O-C-H. 

H H H H 

These are the only ways in which two carbon atoms, six 
hydrogen atoms, and one oxygen atom can be combined, if the 
rules of valency are to be observed ; and it is a matter of chemical 
experience that two, and only two, compounds of the formula 
C 2 H 6 O exist. In order to decide which formula is to be assigned 
to which of the two compounds, the properties of the latter are 

282 The Rise of Organic Chemistry 

investigated. Thus, one compound of the pair, namely alcohol, 
will react with sodium in such a way that one of its six hydrogen 
atoms is replaced by the metal ; the other five cannot be replaced 
by sodium by any known treatment. The deduction chemists 
draw from this fact is that, in the molecule of alcohol, one of the 
six hydrogen atoms must be in a unique position, different from 
thekind of position occupied by the other five. Formula (i) shows 
such an arrangement, for one of the hydrogen atoms is attached 
to oxygen, while the other five are attached to carbon. In 
formula (ii), on the contrary, all six hydrogen atoms are in exactly 
equivalent positions. For this reason, and others of a similar 
kind, formula (i) is assigned to alcohol. The general procedure in 
determining the architecture of an organic molecule is to in- 
vestigate as fully as possible the reactions of the compound and 
then to construct a tentative formula that expresses them. 
Such an analysis is followed, if possible, by the synthesis of a 
compound known to have the formula so deduced . If the synthetic 
product proves to be identical with the original substance, the 
formula is fully established. Thus, in the case of alcohol, we 
can easily prepare a compound known to have the structure 

H H 

H H 
by taking ethane, 

H H 



the formula for which is unambiguous, treating it with chlorine 
to form ethyl chloride, 

H H 


I I 
H H 

The Rise of Organic Chemistry 283 

and acting upon this with caustic soda, when 



-O-H = H-C-C-O-H + NaCl. 

H H H H 

The compound thus synthesized turns out to be alcohol, the 
constitution of whose molecule, originally deduced by analysis, 
has thus been confirmed by synthesis. 

In the formula of alcohol a short 'carbon chain' will be 
noticed, consisting of two carbon atoms linked together. This 
is a very simple example of such a structure, but there appears 
indeed to be no limit to the number of links a carbon chain may 
contain. In paraffin wax, for instance, there may be as many as 
sixty carbon atoms in the chain, while in mutton-fat there are 
fifty-seven, and these are by no means among the most complex 
of organic substances. The potentialities of carbon as the parent 
substance of derivative compounds are thus practically illimi- 
table, and already nearly half a million organic compounds have 
been prepared. Some of the most interesting, as well as the most 
valuable, contain a skeleton of carbon atoms of peculiar forma- 
tion, in which the ends of the 'chain' have joined up together to 
form a 'ring'. The prototype of this class of compounds is the 
hydrocarbon benzene, C 6 H 6 , which was discovered in 1825 by 
Faraday. Benzene has very different properties from those of 
other organic substances of apparently similar structure (e.g. 
C 6 H 14 ), and Kekule found it impossible to devise an ordinary 
chain formula for its molecule. One evening, however, he was 
dozing in front of the fire, and dreamt of the dance of the atoms. 
'My mental vision,' he said 'rendered more acute by repeated 
visions of the kind, could now distinguish larger structures, of 
manifold conformation: long rows, sometimes more closely 
fitted together; all twining and twisting in snake-like motion. 
But look! What was that? One of the snakes had seized hold of 
its own tail, and the form whirled mockingly before my eyes. 
As if by a flash of lightning: I awoke ; and this time also I spent 

284 The Rise of Physical Chemistry 

the rest of the night in working out the consequences of the 
hypothesis.' Kekule thus conceived the idea that in the mole- 
cule of benzene the six carbon atoms, instead of forming an 
open chain, have joined together to form a six-membered ring. 
This hypothesis he expressed in the formula 

a b c d e f 

I I I 

c- c-c- c-c = c 

where a, b, c, d, e, and / represent the positions of the six 
hydrogen atoms. Later, he wrote the formula 



UC^ \CH 

i I! 


\ c / 


which may be contrasted with the formula of an 'open-chain' 
compound containing the same number of carbon and hydrogen 
atoms : 

CH 2 - CH-C EE C-CH = CH 2 

All subsequent investigation has confirmed the 'ring' structure 
of the benzene molecule, and if we remember that perhaps half 
the total number of organic compounds at present known are 
derivatives of benzene we shall form a just estimate of the value 
of Kekule's work. 

Vast as has been the expansion of organic chemistry since the 
publication of his classical Lehrbuch, the theoretical framework 
of the subject has remained materially as he left it. We may 
therefore take leave to pass on to the story of the rise of physical 
chemistry which, though scarcely half a century old, has 
justified its claim to autonomous rank. 

57. The Rise of Physical Chemistry 

CHEMISTRY and physics form two adjacent territories between 
which there is no well-defined line of demarcation. The study 

The Rise of Physical Chemistry 285 

of those topics that lie in the 'no man's land', the application of 
physical methods to chemical problems, and the use of chemical 
data in physics, have led to the establishment of an intermediate 
branch of science known as 'physical chemistry'. The elemen- 
tary distinction between chemical changes and physical changes, 

Fig. 92. VAN'T HOFF 

so earnestly impressed upon us in our school-days, is an entirely 
arbitrary one and breaks down as soon as we bear upon it a little 
heavily. Chemistry and physics both deal with the properties 
of inanimate matter, and are but different methods of approach 
to the same objective. Particularly is this true in such matters 
as the effect of electricity upon bodies, the structure of the atom, 
the thermal concomitants of chemical reactions, the optical and 
magnetic properties of substances, the chemical action of light, 
and radioactivity. To attempt to deal with problems such as 
these from a purely chemical or purely physical point of view is 

286 The Rise of Physical Chemistry 

clearly an impossibility, and recognition of this fact was made in 
1887, when Ostwald and van't Hoff founded the Zeitschrift fiir 
physikalische Chemie or 'Journal of Physical Chemistry*. 

The principal focus of physical chemistry in its early days was 
the nature of solutions. We saw in an earlier section that solu- 
tions of acids, bases and salts conduct electricity, by the passage 
of which they are decomposed. Most organic substances, on the 
contrary, form solutions that do not conduct the current. The 
reasons for such disparity of behaviour have formed an in- 
exhaustible subject of investigation, from the time of Faraday 
(1791-1867) to the present day. Faraday 's own contributions 
were of fundamental importance. In his Experimental Researches 
in Electricity (1831-8) he enunciated his celebrated Laws of 
Electrolysis, according to which 

i. The weight of a substance liberated in electrolysis is pro- 
portional to the quantity of electricity that has passed through 
the electrolyte (i.e. conducting solution); and 

ii. When the same quantity of electricity is passed through 
different electrolytes, the weights of the substances liberated are 
in the ratio of their chemical equivalents. 

These laws afforded a striking confirmation of the views of 
Berzelius and Davy upon the intimate connexion between 
electrical and chemical forces, and incidentally foreshadowed 
the 'atomic' theory of electricity. From the chemical standpoint, 
however, they remained comparatively unproductive until 
Raoult, in 1884, drew attention to the marked contrast in other 
physical properties shown by conducting and non-conducting 
solutions. Raoult observed, among other things, that electro- 
lytes 1 exhibited anomalous behaviour in their effect upon the 
depression of the freezing-point of a solvent in which they were 
dissolved, and upon the elevation of its boiling-point, the 
abnormality in each case being of such a nature that the effect 
produced was greater than would have been expected. Now the 

1 The word electrolyte now signifies a substance that, in solution or in the 
liquid or fused state, will conduct electricity at the expense of its own 

The Rise of Physical Chemistry 287 

phenomena mentioned are conditioned by the molecular con- 
centration of the solute in the solvent, so that Raoult's results 
seemed to indicate that, in a solution of an electrolyte, there 
were more molecules of solute than had actually been in- 

It was left to Arrhenius (1859-1927) to gather up both the 


normal phenomena of electrolysis and this abnormal behaviour 
of electrolytes in a comprehensive theory known as the Theory of 
Electrolytic Dissociation. One of the earliest papers in the 
Zeitschrift fur physikalische Chemie contained an account of this 
theory, which, after a period of neglect and opposition, finally 
won an almost universal acceptance seasoned, it is true, by 
a few examples of complete scepticism. 

Arrhenius suggested that when an electrolyte is dissolved in 
water it splits up, almost completely in dilute solution and to 

288 The Rise of Physical Chemistry 

a less extent in concentrated solution, into charged atoms or 
groups of atoms, which (by a transference of a name first used 
by Faraday) were called ions. During electrolysis, the current is 
carried by the ions, which are themselves attracted to the 
positive or negative electrode, according to whether the charge 
they carry is negative or positive. On reaching the electrodes, 
the ions give up their charges and become converted into 
ordinary atoms or groups of atoms, which may or may not 
appear as such : if they do not attack water chemically they may 
remain unaffected, but if they do, then secondary products will 
make their appearance. Each ion, according to Arrhenius, was 
supposed to exert the same effect upon the depression of the 
freezing-point of the solvent, and the elevation of its boiling- 
point, as an ordinary undissociated molecule. 

The theory thus provided a coherent and intelligible explana- 
tion of entirely distinct categories of facts, an infallible criterion 
of its worth. Yet it was of such a revolutionary character that its 
merits remained unperceived, and had it not been for the efforts 
of the German chemist Ostwald, Arrhenius might have 
succumbed to the same kind of treatment as that which proved 
fatal to Newlands. To appreciate some of the objections that 
were levelled against the theory, let us consider a definite 
example. If Arrhenius is to be followed, a small quantity of salt 
when dissolved in a large quantity of water suffers a scission of 
practically the whole of its molecules into positively charged 
sodium atoms, or sodium ions, and negatively charged chlorine 
atoms, or chlorine ions. Should an electric current now be passed 
through the solution, the sodium ions are attracted to the negative 
electrode or cathode, and the chlorine ions to the positive 
electrode or anode. Here they give up their charges and become 
converted into ordinary sodium and chlorine atoms. But 
sodium acts upon water, forming caustic soda and hydrogen, 
the former remaining in solution while the latter is evolved as 
a gas. Chlorine, on the contrary, does not readily attack water, 
and is therefore evolved as a gas from the anode. 

It is essential to distinguish here between the observed facts 

The Rise of Physical Chemistry 289 

and the hypothetical explanation of them. The formation of 
caustic soda, and the liberation of hydrogen and chlorine, upon 
electrolysis of a solution of common salt, are experimental facts 
about which no disagreement is possible ; but that such a solu- 
tion, whether subjected to electrolysis or not, contains myriads 
of highly charged sodium atoms and chlorine atoms is merely 
an hypothesis. We cannot feel surprised that so extraordinary a 
suggestion met with scant attention at first and then with violent 
opposition. Critics objected that it was ridiculous to imagine 
the presence of free atoms of sodium (a metal that vigorously 
attacks water) and of chlorine (a poisonous, yellowish-green gas 
with a pungent smell and great chemical and physiological 
activity) in a solution of so innocuous a substance as common 
salt. This criticism, however, really rests upon a misunderstand- 
ing of the theory. Arrhenius's hypothesis was that these free 
atoms are indeed present, but that they are each carrying an 
intense electric charge. There is no difficulty in assuming that 
highly charged atoms, or ions, have very different properties 
from those possessed by the same atoms uncharged, for it is 
a matter of common experience that objects carrying a charge 
of electricity show peculiarities of behaviour. When this point 
was made clear, much of the original opposition was silenced, 
and Arrhenius and his followers were able to show that many 
perplexing properties of aqueous solutions found a satisfactory 
explanation in terms of the theory of electrolytic dissociation. 
In its primitive form, the theory is now obsolete, but it has 
formed the basis of all subsequent work in this province, and its 
main dogmas are incorporated in the current doctrines of 

The greater part of physical chemistry is of a mathematical 
and technical complexity that does not lend itself to summary 
description, and as it is of such recent growth as to be almost 
contemporary it falls without our present limits. Yet since we 
witnessed the birth of the classical Atomic Theory, we may 
perhaps permit ourselves to assist at the unfolding of the greatest 
of all physico-chemical themes, namely the structure of the atom. 

2613-4 n 


58. The Structure of the Atom 

FOR nearly a hundred years, Dalton's atomic theory held un- 
disputed sovereignty. Master and slave alike, the indivisible 
atom ruled the destiny of chemistry and was also the means of 
its fulfilment. In this twentieth century, however, the Daltonian 
atom is an out- worn conception, whose place has been taken by 
a congeries of units of positive and negative electricity. A con- 
sideration of the latest views on the structure of the atom does 
not lie within the scope of the present book, but the revolution 
in chemical thought during the last thirty years has been so pro- 
found that we may conclude our story with an account of the 
work that led to it. 

In 1896 Becquerel showed that uranium salts have the power 
of acting upon a photographic plate even when the latter is 
wrapped in black paper. Compounds of thorium behave in the 
same way, and as the effect was believed to be caused by an 
emission of 'rays', uranium and thorium compounds were de- 
scribed as radioactive. Whilst examining the uranium mineral 
pitchblende, Madame Curie found indications of the presence 
of a much more powerfully radioactive body in it. She success- 
fully devised methods of extracting this substance and showed 
that it was a new element, which she isolated in the form of a 
mixture of its bromide with barium bromide. This new element 
was called radium. By fractional crystallization from alcohol it 
was found possible to separate the radium bromide from the 
barium bromide, and in 1910 metallic radium was prepared by 
the electrolysis of a solution of radium chloride, using a mercury 
cathode. The radium liberated at the cathode dissolved in the 
mercury to form an amalgam, whence the mercury was distilled 
off, leaving the radium as a white metal which quickly rusts in 
the air, and which, like calcium and barium, acts upon water in 
the cold with evolution of hydrogen. 

Radium salts will discharge an electroscope, and investiga- 
tion of this property led to the discovery that radium gives off 
three different kinds of rays, called respectively the a-, /3- 

The Structure of the Atom 291 

and y-rays. The nature of these radiations will be discussed 

Metals, and solutions of acids, bases and salts in water and 
certain other solvents, conduct electricity, but gases under 
ordinary pressures are non-conductors unless high potentials 




are employed. If, however, the pressure is lowered, it is found 
that gases begin to conduct more easily, but at still lower pres- 
sures exceedingly high potentials must be employed to drive the 
discharge through. The phenomena of conduction are very 
characteristic. At a pressure of o-oi mm. a phosphorescence is 
produced on the walls of the glass tube opposite the cathode. 
The nature of this phenomenon was investigated by Sir William 
Crookes, who showed that the phosphorescence was caused by 
a stream of exceedingly minute negatively electrified particles 
which he called the Cathode Rays. 

The cathode rays are deflected by electric or magnetic fields 
in exactly the way that would be expected of a stream of 
negatively charged particles, and are capable of passing through 
thin plates of various metals. In 1895 Rontgen showed that 
from the phosphorescent spot produced by allowing cathode 
rays to strike upon the end of the vacuum tube in which they 
were formed, another beam of rays was projected, of great 
penetrating power. These rays he called X-rays. 

The particles of which the cathode rays consist are known as 
[negative] electrons. Each electron has a mass of about T^ 

u 2 

292 The Structure of the Atom 

of that of a hydrogen atom, and carries a charge equal (but 
opposite in sign) to that carried by a hydrogen ion. 

It has been shown that X-rays are similar to light vibrations 
except that their wave-lengths are very much smaller ; they can 
be diffracted and polarized by suitable means. The beam of 
X-rays produced from an ordinary X-ray tube consists of a 
mixture of rays of different wave-lengths, in the same way that 
white light consists of a mixture of light rays of different wave- 
lengths. A very important fact is that every element is capable of 
emitting X-rays of wave-lengths peculiar to itself, if stimulated in 
an appropriate way. Such a way is to allow X-rays of a shorter 
wave-length to strike the substance, when the latter at once 
gives off its characteristic radiation. Now, just as the ordinary 
spectrum of an element is mapped and measured by means of a 
spectrometer, so it is possible to map and measure the X-ray 
spectrum of a substance by means of an instrument called the 
X-ray spectrometer. 

To understand how this works it is necessary to know the 
principle of a device called the diffraction grating. If ordinary 
white light is passed through a prism it is split up into light of 
various wave-lengths, and a spectrum may be produced. This 
analysis of light can also be brought about by another arrange- 
ment called the diffraction grating, which consists of a large 
number of very fine parallel lines accurately drawn upon a plane 
sheet of glass in such a way that the spaces separating the lines 
are all equal. Light which falls on this grating is 'diffracted' or 
bent out of its normal path through an angle which is constant 
for a given wave-length of light but which differs for different 
wave-lengths, so that the grating 'sorts out' the light into 
a spectrum. If the width of the space between two lines of the 
grating is known, it is possible to calculate the wave-length of 
any line in the spectrum, and it is in this way that the wave- 
lengths of rays of light are measured. 

X-rays are of the same nature as light-rays, but the wave- 
lengths of light-rays are several thousand times greater than 
those of the X-rays. Hence the ordinary diffraction gratings are 

The Structure of the Atom 293 

much too coarse to be of any use for the purpose of forming an 
X-ray spectrum and measuring the wave-lengths of the various 
lines . However, in 1 9 1 2 Laue ( 1 879- ) suggested that the atoms 
in a crystal might serve as the lines of a diffraction grating, and 


the spaces between two consecutive parallel planes of them as the 
spaces of the grating. If this is so, then a crystal forms a natural 
diffraction grating which should apparently be of suitable 
dimensions for giving an X-ray spectrum. Upon investigation 
this was found to be the case. When X-rays fall on a crystal they 
are diffracted in exactly the same way as light is by an ordinary 
diffraction grating. Hence, to measure the wave-length of X- 

294 The Structure of the Atom 

rays, all we need to know is the distance between the planes of 
atoms of a particular crystal. Fortunately it has been found 
possible to calculate this distance, and therefore to find the actual 
wave-length of any X-ray. 

The X-ray spectrometer (Fig. 95) makes use of the fact that a 
crystal will act as a diffraction grating for X-rays. The X-rays 
to be examined are passed through a slit in a sheet of lead and 
then through a second slit that serves to cut off any scattered 
radiations. The pencil of rays then impinges on and is diffracted 
from a crystal fixed by means of a piece of wax on a horizontal 
arm that can revolve on a vertical axis over a graduated circle. 
After diffraction from the crystal the X-rays are made to pass 
through a third slit into a tube containing a gas which is easily 
'ionized' (or made to conduct) by the rays; sulphur dioxide is 
commonly used for the purpose. In this 'ionization chamber' is 
an electrode (placed in such a position that the X-rays entering 
the chamber do not strike it) connected to an electroscope. The 
ionization chamber is mounted on a horizontal arm which can 
revolve around the same axis as that on which the crystal is 

To conduct the experiment, the X-rays are diffracted from 
the crystal and the ionization chamber turned until an X-ray 
passes into it, causing the gas inside the chamber to become 
ionized ; this is indicated by the electroscope. The angle through 
which the ionization chamber has been turned is noted, and the 
latter is then moved still farther until the next X-ray passes into 
it, as shown by the electroscope. 

In this way the X-ray spectrum of the substance under 
observation can be measured, and the intensity of any given line 
in the spectrum is indicated by the degree to which the electro- 
scope is affected. 

If a pencil of X-rays is passed through a crystal and then on 
to a photographic plate, spots are produced on the plate, 
arranged in a symmetrical way. These spots are caused by the 
scattering of the X-rays by the atoms in the crystal, and by con- 
structing space-models from the photographs it has been found 

The Structure of the Atom 295 

possible to determine the spatial arrangement of the atoms 
within the crystal. Thus Sir W. H. and Professor W. L. Bragg 
have shown that the atoms in a crystal of potassium chloride are 
arranged in the way shown in Fig. 96, the potassium atoms being 
represented by black circles and the chlorine by white O . 
The atoms of carbon in the diamond are arranged in groups of 


six in such a way that each carbon atom is at the centre of the 
regular tetrahedron formed by the four atoms nearest it. 

The method has recently been extended to liquids, and the 
shape and even the size of the benzene molecule have been de- 
termined. The shape is that of a regular hexagon, of side 
0-0000000602 cm. and thickness 0-0000000119 cm. 

Let us return now to the a-, /?- and y-rays emitted by radium. 
It has been shown that the a-rays consist of positively charged 
particles of atomic dimensions, and of atomic weight 4. Each 
carries two unit positive charges. The -rays consist of negative 
electrons moving with a very high velocity, while the y-rays are 
X-rays of very short wave-lengths. These rays are produced by 
the disintegration of the radium atoms. The atomic weight of 
radium is 226 ; when one atom of radium gives off an a-particle 
of atomic weight 4, an atom of atomic weight 222 should be left. 
This is actually the case. It has been shown that the a-particle 

296 The Structure of the Atom 

is an atom of helium carrying two unit positive charges, while th< 
Element' of atomic weight 222 has been isolated and is callec 
'radium emanation' or radon. Radon itself is radioactive anc 
splits up into helium and a solid substance called the *activ( 
deposit', which is still radioactive. 

This spontaneous disintegration of atoms led scientists t( 
formulate hypotheses on the structure of the atom, since atoms 
were clearly no longer to be considered as indivisible. Man) 
suggestions were made, but that which agreed best with observec 
facts considered the atom to consist of an exceedingly minute 
positively charged nucleus surrounded by a number of elec- 
trons that revolve in more or less spherical orbits around the 
nucleus. Bragg showed that the a-particles emitted frorr 
radium could pass through thin sheets of solid substances, anc 
proved that in doing so they pass not only through the spaces 
between the atoms of these substances, but also actually through 
the atoms themselves if these happen to be on their path. Wher 
the a-particles pass through atoms most of the particles are nol 
deflected from their rectilinear path, but a small number of their 
suffer large deflections. This phenomenon is explained by 
assuming that when an a-particle passes through an atom and is 
not deflected thereby, it has not gone near the nucleus but only 
through the outer regions of the atom those in which the 
electrons revolve in their orbits. If we compare the atom 
to our solar system we could regard the sun as the positive 
nucleus and the planets as the electrons ; now it is conceivable 
that a foreign sun might rush through our solar system and 
still not come anywhere near the Sun. It seems that the 
chances of an a-particle coming within close range of the nucleus 
of an atom are about equally unlikely. When, however, an 
a-particle does happen to pass close to the nucleus of an atom 
it is violently deflected. In Lord Rutherford's words, 'to 
account for these results, it was found necessary to assume 
that the atom consists of a charged massive nucleus of dimen- 
sions very small compared with the ordinarily accepted magni- 
tude of the diameter of the atom. This positively charged 

The Structure of the Atom 297 

nucleus contains most of the mass of the atom, and is surrounded 
at a distance by a distribution of negative electrons equal in 
number to the resultant positive charge on the nucleus. Under 
these conditions, a very intense electric field exists close to the 
nucleus, and the large deflection of the a-particle in an encounter 
with a single atom happens when the particle passes close to the 
nucleus. Assuming that the electric forces between the a- 
particle and the nucleus varied according to an inverse square 
law in the region close to the nucleus, [Lord Rutherford] 
worked out the relations connecting the number of a-particles 
scattered through any angle with the charge in the nucleus and 
the energy of the a-particle. Under the central field of force, 
the a-particle describes a hyperbolic orbit round the nucleus, 
and the magnitude of the deflection depends on the closeness of 
approach to the nucleus. From the data of scattering of a- 
particles then available, it was deduced that the resultant charge 
on the nucleus was about J A e y where A is the atomic weight and 
e the fundamental unit of charge [i. e. e is equal in magnitude to 
the charge carried by a single negative electron]. . . . 

* Since the atom is electrically neutral, the number of external 
negative electrons surrounding the nucleus must be equal to the 
number of units of resultant charge on the nucleus. It should be 
noted that, from consideration of the scattering of X-rays by 
light elements, Barkla had shown, in 1911, that the number of 
electrons was equal to about half the atomic weight. . . . 

'Two entirely different methods had thus given similar results 
with regard to the number of external electrons in the atom, but 
the scattering of a-rays had shown in addition that the positive 
charge must be concentrated on a massive nucleus of small 
dimensions. It was suggested by van den Broek that the scatter- 
ing of a-particles was not inconsistent with the possibility that 
the charge on the nucleus was equal to the atomic number of the 
atom, i. e. to the number of the atom when arranged in order of 
increasing atomic weight/ taking hydrogen as i, helium as 2, 
lithium as 3, and so on. 

It will be convenient here to consider the results of an in- 

298 The Structure of the Atom 

dependent line of research carried out by Moseley, who in- 
vestigated the X-ray spectra of various elements by means of the 
X-ray spectrometer. He found that the X-ray spectra obtained 
in this way show two strong lines for each element, accompanied 
by a number of weaker lines (see Fig. 97). Of the two strong lines, 
one is stronger than the other and is called the a-line, while the 
weaker is called the /Mine. It has been shown that if v is the 
frequency (i.e. number of vibrations per second) of the a-line, 
and TV the atomic number of the element, then 

i) = %(N i) 2 a constant. 

This constant is called Rydberg's constant and its value is 
known. If, therefore, we measure the frequency of the a-line of 
the X-ray spectrum of an element, we can calculate the position 
which it ought to occupy in the Periodic Table, that is, its 
Atomic Number. 

This important discovery made it possible for the first time to 
call the roll of the chemical elements and to determine how many 
there were and how many remained to be discovered. There 
are between and including hydrogen and uranium ninety-two 
possible elements, of which only two (1931) remain to be found. 

Moseley's work, in fact, showed that the 'properties of an 
atom were defined by a number which varied by unity in 
successive atoms. This gives a new method of regarding the 
periodic classification of the elements, for the atomic number, 
or its equivalent the nuclear charge, is of more fundamental 
importance than its atomic weight.' Most of the physical and 
chemical properties of an atom depend upon the number 
and arrangement of the electrons in the atom, and these will 
clearly depend upon the charge on the nucleus. In other words, 
the actual mass of the atom is of secondary importance. 

Hence we are led to the conclusion that 'it is quite possible to 
imagine the existence of elements of almost identical physical 
and chemical properties, but which differ from one another in 
mass, for, provided the resultant nuclear charge is the same, 
a number of possible stable modes of combination of the 

The Structure of the Atom 299 

different units which make up a complex nucleus may be 
possible/ In other words, we may get atoms which are chemi- 
cally indistinguishable and yet of different atomic weights. Are 
we to regard such atoms as atoms of different elements, or as 
atoms of the same element? According to Dalton, all the atoms 


of the same element have the same atomic weight; hence 
from this point of view atoms that are chemically identical but 
have different atomic weights belong to different elements. On 
the other hand, chemical considerations would lead us to regard 
atoms that are chemically identical as atoms of the same 
element. Soddy gave the name isotopes or isotopic elements to 
those elements which fall into the same place in the periodic 
system, and are chemically identical, but have differing atomic 

We have already seen that when an a-particle (or helium atom 
carrying two positive charges) is expelled from a radium atom, 
the product (radon) is an element which falls into Group O of 
the periodic system, or two columns to the left of that in which the 
parent radium atom is placed. Study of other radioactive pro- 

300 The Structure of the Atom 

ducts has shown that this is a general phenomenon expulsion 
of an a-particle from the atom of an element in Group *N* re- 
sults in the formation of an atom of an element which falls into 
Group 'N-2* and has an atomic weight differing by four units 
from that of the parent atom. Further investigation has pro- 
duced evidence to show that when one ^-particle is expelled 
from the atom (probably from the nucleus), an atom is formed 
which is that of an element that falls into a column one to the 
right of that in which the parent element is placed, but of the 
same atomic weight. 'Each of the successive places in the periodic 
table thus corresponds with unit difference of charge in the con- 
stitution of the atom/ a conclusion previously arrived at by van 
den Broek. We see, too, that there is, in addition to the existence 
of isotopes, a possibility of the existence of different elements 
with the same atomic weight: these have been called isobaric 
heterotopes. Elements which differ in chemical properties and 
also in atomic weight have been called heterobaric heterotopes. 
All heterotopes are separable by chemical means. 

The existence of isotopes suggested above is rendered still 
more probable by the following considerations. Suppose an 
atom loses an a-particle by radioactive change. We have seen 
that an atom will be formed of atomic weight four units less, and 
belonging to an element two columns to the left in the periodic 
table. Suppose now this daughter-atom loses two ^-particles. 
It will have moved two places to the right in the table and will 
therefore have reached the position from which it set out, with 
no further change in atomic weight. We should now have two 
atoms differing by four units in atomic weight, but absolutely 
identical in chemical properties, that is, they are isotopic elements, 
or isotopic forms of the same element with different atomic 
weights. Fig. 98 will make this clear. 

It will be seen that atoms A and B occupy the same position 
in the table, and are chemically identical; but they differ in 
atomic weight by four units: they are isotopes. C and D are 
isobaric heterotopes. 

The first case in which these views were tested experimentally 

The Structure of the Atom 301 

was that of lead. It had been proved that the end-products of 
the radioactive disintegrations of thorium and of uranium both 
fell into the place in the periodic table occupied by lead, but a 
consideration of the intermediate stages led to the conclusion 
that the lead derived from uranium should have an atomic 

Group N+1 


weight of 206, while that from thorium should have an atomic 
weight of 208. Now uranium minerals often contain small 
quantities of lead, and it is reasonable to suppose that this lead 
has been derived from uranium by radioactive changes; 
similarly, the lead found in thorium minerals has probably been 
derived from thorium. Lead was extracted from both these 
sources, and the atomic weights of the specimens were carefully 
determined by chemists skilled in atomic weight determinations. 
It was found that the lead from uranium minerals had an atomic 
weight of 206-05 and that from thorium minerals 207-9. Thus 
the theory was triumphantly justified. Ordinary lead, of atomic 
weight 207-2, is a mixture of these isotopes in the appropriate 
proportion. The 206-05 lead and the 207-9 ^ eac ^ wer ^ proved 
to be chemically identical, as predicted by the theory. 

Further investigations have shown that many other elements 
are heterogeneous, that is, the 'element' as ordinarily encountered 

302 The Structure of the Atom 

is a mixture of isotopes. A very significant fact is that in every 
case the atomic mass of a pure isotopic element is a whole 
number, taking O = 16-00 as the standard of comparison. To 
afford an explanation of this arresting phenomenon, it was 
suggested that the nuclei of other atoms are composed of 
hydrogen nuclei and helium nuclei. This theory has received 
support from work of Lord Rutherford, who was able to 
show that by bombarding nitrogen atoms with swiftly moving 
a-particles it is possible to disintegrate a few of the former, one 
of the products of disintegration being positively charged 
hydrogen atoms. 

Here we stand upon the threshold of present-day research, 
and must at length part company. If our long association has 
done nothing else, it will at least have taught us a juster apprecia- 
tion of chemical achievement, which, as old Geber put it, 
demands 'a Natural Ingenuity, and Soul, searching and subtily 
scrutinizing Natwal Principles, the Fundamentals of Nature, and 
Artifices which can follow Nature, in the properties of her 
Action 9 . 


Abu'l-Qasim al- c lraqi, 81-2. 

Abu Mansur Muwaffak, 67-8. 

Adelardof Bath, 84, 88. 

Adet, 216, 244. 

Agatharchides, 7. 

Agathodemon, 46. 

Aidamir al-Jildaki, 52, 56, 75, 81-2. 

'Ala al-Daula, 70. 

Alexander of Aphrodisias, 68. 

Alexander the Great, 16, 32, 46, 48. 

Alfred the Englishman, 72, 86, 91. 

Ali al-Rida, 56. 

Ali, Caliph, i, 43. 

Ali ibn Sahl, 64. 

Al-Jildaki, 52, 56, 75, 81-2. 

Al-Juzjani, 70. 

Al-Khwarizmi, 87. 

Al-Ma'mun, 52, 56. 

Alston, Dr., 166. 

Al-Tughra'i, 75. 

Apollonius, 32, 54, 78. 

Aquinas, Thomas, 90. 

d'Arcet, see Darcet. 

Archimedes, 32. 

Aristotle, i, 16-21, 22, 23, 32, 33, 

39, 54, 56, 58, 67, 68, 69, 70, 78, 

88, 90, 96. 

Armstrong, H. E., 208. 
Arnold of Villanova, 89, 98. 
Arnold, Sir Thomas, 41. 
Arrhenius, 287-9. 
Assurbanipal, 13. 
Averroes, 91. 
Avicenna, 68-77, 8 3, 9, 9 l > 9 2 , 97, 

100, 101, 109. 
d'Avisonne, see Davidson. 
Avogadro, 121, 249-57, 258, 278. 

Bacon, Francis, 134. 

Bacon, Roger, 81, 89, 90-8, 104. 

Baeyer, Adolf von, 273. 

Bailey, Cyril, 217. 

Banks, Sir Joseph, 177, 259. 

Barkla, 297. 

Bartholomew the Englishman, 98- 


Basilides, 33. 
Bauch, 187. 
Baume'. 217. 

Beauvais, Vincent de, 89-90. 
Becher, 20, 141, 143-150, 154. 
Becquerel, 290. 
Be"guin, Jean, 128. 
Bergman, 208. 
Bernouilli, Jean, 160. 
Berthelot, 30, 35, 48, 104. 
Berthollet, 200, 211, 214, 236. 
Berzelius, 238, 239, 240-8, 249, 257, 

259-60, 261-3, 274, 275, 276, 279, 


Biwan the Brahman, 27. 
Black, Joseph, 164-9, T 76, 179, 192, 


Blagden, 200. 
Boerhaave, i, 161, 179, 
Boyle, 67, 122, 124, 131, 132-43, 

153-4, 156, 160, 201, 203, 218, 

219, 220, 263. 

Bragg, Sir W. H., 295, 296. 
Bragg, W. L., 295. 
Breughel, Peter, 119. 
Brosse, Guy de la, 128. 
Brown, Crum, 281. 
Brun, Sieur, 151-2. 
Buffon, 191. 
Burke, 170. 

Cannizzaro, 256, 266, 278. 

Cardanus, 151. 

Carlisle, 259. 

Carra de Vaux, 68, 75. 

Cavendish, 130, 164, 177-86, 189, 

197, 200, 209. 
Champollion, 6. 
Chandler, John, 120. 
Charlemagne, 103, 
Charles the Hammer, 41. 
Cleopatra, i. 
Coffinhal, 213. 
Cohen, J.B., 156. 
Crivelli, 6. 

Crookes, Sir William, 291. 
Cullen, William, 164-6. 
Curie, Madame, 290. 

Dalton, 22, 23, 121, 221-40, 244, 
246, 248, 249, 252-4, 256, 257, 

2<?8. 2QO. 2QQ. 


Index of Names 

Dalton, Jonathan, 221. 

Darcet, 192, 200. 

Davidson, William, 128. 

Davy, Sir Humphry, 1 89, 227 -8, 242, 

260-1, 286. 

Democritus, i, 21, 36, 44, 46, 54. 
Descartes, 217, 218. 
Desch, 5. 
Diderot, 198. 
Diocletian, 29-30. 
Diodorus Siculus, 7. 
Dobereiner, 264-5. 
Dudu, 12. 
Dumas, 215, 264, 277-8. 

d'Eldment, Moitrel, 160. 
Empedocles, 23, 54. 
Enlil, 12. 

Entemena, n, 12. 
Epicurus, 21, 217. 
Erasmus, 1089. 
Eratosthenes, 32. 
Euclid, 32, 54. 

Faraday, 283, 286, 288. 
de Faye, 33. 
Fischer, Emil, 188. 
Fourcroy, 211, 214. 
Frankland, Sir Edward, 278, 280. 
Franklin, Benjamin, 200. 
Frobenius, Johannes, 108-9. 
Fugger, Sigismund, 108. 

Galen, 27, 109. 

Galileo, 67, 249. 

Gamble, 259. 

Garland, 5. 

Gassendi, 21718. 

Gay-Lussac, 121, 186, 2504, 259. 

Geber, see Jabir ibn Hayyan. 

Gerard of Cremona, 84, 88. 

Gerhardt, 278. 

Gibbon, 29. 

Gilbert, Davis, 227-8. 

Glaser, Christopher, 128. 

Glauber, 184, 195. 

Gmelin, 275. 

Gossage, 259. 

Graecus, Marcus, 104. 

Graham, 246. 

Grimm, 191. 

Grossette, 92. 

Gudea, 12. 

Gunther, Dr., 143. 

Hales, Stephen, 122, 161. 

Harbi al-Himyari, 50. 

Harun al-Rashid, 50, 52, 54. 

Haskins, C. H., 84. 

Hassenfratz, 216, 244. 

Hatchett, 178. 

Hathor, 7. 

Hayyan, 49-5- 

Heliodorus, 39. 

Heraclius, 46. 

Hermann the Dalmatian, 86, 88. 

Hermes, i, 2, 35, 46, 104, 114. 

Hipparchus, 32. 

Hippocrates, 54. 

Hisinger, 259. 

Hoefer, 121, 189. 

Hooke, Robert, 155, 156, 219. 

Hunain ibn Ishaq, 75. 

lamblichus, 33. 
Ibn Abi Usaybi'a, 70. 
Ibn al-Nadim, 52. 
Ibn Arfa' Ra's, 76. 
Ibrahim, 69. 
Ingenhousz, Dr., 178. 
Isidore, 100. 

Jabir ibn Hayyan, 49-63, 66, 70, 73, 
78, 79, 81, 82, 83, 84, 90, 92, 101, 
106, 132, 143, 144, 151, 184, 302. 

Ja'far al-Sadiq, 50, 52. 

Jason, i. 

Joachim, 20-1. 

Johnson, O. S., 24. 

Kanada, 27. 

Kekule, 256, 278, 280-1, 283-4. 

Khalid ibn Yazid, 43-4, 52, 79, 82. 

Khammurabi, 13. 

Khayyam, Omar, 217. 

Kirwan, Richard, 183, 211, 212. 

Ko Hung, 24-5. 

Kopp, 256. 

Lagercrantz, 30. 

Lagrange, 200, 213. 

Langdon, S. H., ir. 

Laplace, 200. 

Laue, 293. 

Laurent, 278. 

Lavoisier, 58, 78, 140, 155, 156, 158, 

176, 177, 183, 192, 196, 197-213. 

214, 215, 216, 221, 236, 257, 258, 

261, 263, 274, 276. 
Lefe"bure, Nicolas, 128. 

Index of Names 


Leibnitz, 124. 

Lemery, 124-31, 132, 133, 152, 187. 

Lepsius, 6. 

Leucippus, 21, 27, 220. 

Libavius, 11719, 120, 132. 

Liebig, Justus von, 275-7, 278. 

Lippmann, E. O. von, 25. 

Locke, John, 143, 219. 

Lucas, 4. 

Lucretius, 21, 22, 23, 24, 217, 220. 

Lully, 89, 98. 

Macquer, 150, 166, 177, 200, 208. 

Magnus, Albertus, 89, 90-8. 

Mansur al-Kamily, 77. 

Marcion, 33. 

Marduk, 13. 

Marianus, 434. 

Mary the Jewess, 46. 

Maslama of Madrid, 77. 

Mayow, 154-8, 160. 

Mellor, J. W., 142. 

Mendeleeff, 268-73. 

de la Metherie, 211. 

Metternich, 256. 

Meyer, Lothar, 257, 268. 

Miriam, i . 

Monge, 211. 

Morveau, Guyton de, 153, 200, 211, 

213, 214, 21516, 208. 
Moseley, 298. 
Moses, i. 

Muhammad, i, 41, 43. 
Muspratt, 259. 

Natih, 69. 

Nebuchadrezzar, 13. 

Nernst, 250. 

Newlands, 266-8, 288. 

Newton, Sir Isaac, 22, 133, 217-21, 


Nicholson, 259. 
Nin-girsu, 12. 
Norton, Thomas, 76. 

Odling, 264. 
Oecolampadius, 108. 
Olympiodorus, 39. 
Ostanes, 44, 46. 
Ostwald, 286, 288. 

Palissy, Bernard, 190. 

Paracelsus, 106-15, 119, 120, 128, 

132, 144, 190. 


Partmgton, 184. 

Paulze, Marie- Anne-Pierrette, 177, 


Pelagius, 39. 
Pelletier, 222. 
Pelouze, 276. 
Peregrinus, Petrus, 93. 
Perignon, Dom, 15960. 
Peter the Venerable, 86. 
Petrie, Sir Flinders, 10. 
Pettenkofer, 264, 265. 
Philalethes, 76. 
Pinas, J., 119. 
Plato, i, 23, 39, 46, 54. 
Plato of Tivoli, 86. 
Pliny, 27. 

Plotmus, 33, 34, 35. 
Porphyry, 33, 35. 
Priestley, 78, 122, 163, 164, 169-77, 

180, 182, 183, 185, 186, 187, 188, 

J97, 2OO, 204, 2O7, 2O8, 2O9, 2IO, 
211-12, 222. 

Proust, 236-7. 
Ptolemy, "54, 78. 
Ptolemy Euergetes, 32. 
Ptolemy Philadelphus, 32. 
Ptolemy Soter, 32. 
Punctis, Madame, 197. 
Pyrophilus, 135. 
Pythagoras, i, 23, 54. 

Ramsay, Sir William, 186. 

Raoult, 286. 

Rayleigh, Lord, 186. 

Razi, 63-7, 78, 82, 83, 90, 112, 132. 

Rey, Jean, 151, 154-5- 

Richter, 239. 

Richthofen, 25. 

Ritter, 259. 

Robert of Chester, 86-9, 92. 

Rontgen, 291. 

Roscoe, Sir Henry, 222. 

Rossellini, 6. 

Rouelle, 164, 189-96, 198. 

Rutherford, Lord, 296-7,^302. 

Rydberg, 298. 

St. John, 2. 

St. Victor, Adam de, 2. 
Sardanapallos, 13. 
Sargon, 12. 
Sayce, 15. 

Scheele, 164, 186-9, J 97> 2O 7> 208, 
242, 274- 


Index of Names 

Shamash, 13 

Shams al-Daula, 70. 

Shelburne, Lord, 169, 176. 

Shem, 2. 

Singer, (Mrs.) Dorothea Waley, 88, 


Smith, Elliot, 7. 
Socrates, 54. 
Soddy, 299. 
Stahl, 20, 141, 143-5) IS 1 * *53> !54> 

158, 194, 211. 
Stapleton, 66-7. 
Steele, Robert, 98. 
Steen, John, 1 19. 
Steno, Nicholas, 72. 
Sthael, Peter, 143. 
Stradanus, John, 119. 
Sultzback, Eck de, 151. 
Synesius, 39. 

Teniers, David, 119. 

Thales, 120. 

Theophrastus, 119. 

Theosebeia, 35. 

Thompson, R. Campbell, 13, 14. 

Thomson, in. 

Thomson, Thomas, 224-7, 238. 

Thorpe, Sir Edward, 187. 

Thoth, see Hermes. 

Tiberius, 100. 

Tiglath-Inurta, 13 

Tilden, Sir William, 250. 
Trithemius, see Trittenheim. 
Trittenheim, Hans von, 108. 
Tubal-Cam, i. 

Ur-Nina, n, 12. 

Valentine, 33. 

Vallot, 128. 

van den Broek, 297, 300. 

van Helmont, 76, 119-24, 128, 132, 


van Ranst, Marguerite, 119. 
van't Hoff, 238, 286. 
Venel, 153. 

Vinci, Leonardo da, 72, 249. 
Volta, 259. 

Warltire, 180. 
Watson, R., 148, 150. 
Watt, James, 200. 
Winckler, 272. 
Wohler, 241-2, 276, 278. 
Wollaston, Dr., 227-8, 238. 
Wurtz, 221, 268. 
Wu Ti, 24. 

Yahya ibn Khalid, 51-2. 
Zosimos, 33, 35-9, 44, 46, 130 


abaru, 47. 

'Abbasids, 50. 

Absorbent earths, 195. 

Acetic acid, 59. 

Acid potassium sulphate, 196. 

Acids, 194. 

Aerial acid, 209. 

Aethiops, 215. 

Affaire Brinvilliers, 128. 

Aim of chemistry, Boyle on, 136. 

Paracelsus on, 112-13. 
Air, 1 6-20. 

consists of two gases, 203-9. 

explosion with hydrogen, 180-1. 

necessary for combustion, 154. 

part played in calcination by, 

Scheele on, 188. 

sparked with clephlogisticated air, 


Al-Azd, 49. 
Alchemical works, false attribution 

of, 46. 
Alchemy, 40, 132. 

Muhammad and, 43. 

Newton's interest in, 219. 

origins of in Islam, 43 -9. 

'practical', 96. 

speculative', 96. 
Alchyniia, 86, 118. 
Alcohol, 14, in, 112, 274. 

constitution of, 2823. 

earliest preparation of, 103. 
Alembic, 66. 
Alexandria, Library not destroyed 

by Muslims, 42. 
Alexandrian School, 32. 
Algebra, of Al-Khwanzmi, 87. 
Alkali, 13. 
Alkalis, 194. 

Black on, 167-9. 
Al-koholy in. 
Al-kufil, in. 
Alluvial gold, 9. 
Almagest, 54, 78. 
Alpha-particle, 295-6. 
Alum, 72, 80. 

used as mordant, 10. 
Alums, in. 

Ammonia, 131. 

formula of, 233. 
anaku, 14. 
Analysis, 282. 
Antimony, 14, 264. 
Apparatus, 38, 118. 
aquafortis, 131. 
aqua regia, 131. 

Arab Arabic-writing Muslim, 42. 
Arabic words, used in Latin alchemy, 

Argill, 264. 
Argon, 1 86. 
Arsenic, 37, 264. 
Arsenious oxide, 68. 
Askalon vessels, 38. 
Asphalt, 12. 
Aspirin, 273. 
Astrolabe, 88. 
athaha, 46. 
atisyus, 46. 

Atom and molecule, distinction be- 
tween, 253-7. 

structure of, 290302. 
Atomic number, 297-8. 
Atomic Theory, 21748. 

chief points of, according to Dalton, 

classical, 214. 

Indian, 27. 

reception of, 227. 
Atomic weights, 233, 248. 

correction of, by Periodic System, 


Atoms, charged with electricity, 

indestructible and uncreatable, 

number of, in, molecules, 234-5. 
aurum potabile, 109. 
Authentic Memoirs (Zosimos), 35. 
Azote, 263. 

Ba-en-pet, 4, 15. 

Balance-room, not in Libavius's 

chemical house, 118. 
Barmecides, fall of, 54. 
Baryta, 264. 
barzel, 15. 

X 2 


Subject Index 

karzi-ili, 15. 
barzillu, 15. 
Benzene, 283-4. 

origin of word, 102. 
Benzoyl radical, 276. 
Bible, contains whole realm of know- 
ledge, 94. 
Bicarbonates, 169. 
Bismuth, in, 264. 
Bleaching action of chlorine, 188. 
Blossom, Book of the, 52. 
Bodies (metals), 67. 
Book of Quintessence, The, 104. 
Book of the Remedy, 70, 91 . 
boracum, 263. 
Brethren of Purity, 77, 81. 
Bronze, 103. 

Cacodyl radical, 277. 
Calces, 147. 

reduction of, 148, 150. 
Calcination, 58-9. 

Boyle on, 153-4. 

increase in weight on, 151. 

of tin and lead, 151. 
Calomel, 196. 
Caloric, 263. 
Calx, 146. 

of mercury, 171-7, 188, 204. 
Canon, of Apollonius, 78. 
Canon of Medicine, 70. 
caput mortuum, 214. 
Carbon, 263. 

chain, 283. 

dioxide, 179, 238. 

action on lime, 167-9. 
formula of, 244. 

essential element in organic com- 
pounds, 274-5. 

oxides, formulae of, 233. 

ring, 283. 

Carbonic acid, 207, 226, 228. 
Carbonic oxide, 226, 228, 238. 
Carburetted hydrogen, 226, 228, 230, 


Cathode Rays, 291. 
Caustic potash, electrolysis of, 


Caustic soda, electrolysis of, 261. 
Ceration, 67. 
chalkanthos, 38. 
Charge against Lavoisier, 199. 
Charlatanry of alchemist, 75-6. 
Chemeia. i*. 

Chemical affinity, 262. 

analysis, 118. 

apparatus, Razi's classification of, 

attraction, related to electrical 
attraction, 260. 

combination, 20, 21. 

industry, 259. 

substances, disco\ered by Scheele, 


Chemicals, classification of in The 
Sage's Step, 79. 

Razi's classification of, 65. 
Chemist, a servant of Nature, 78. 
Chemistry, 'a French science', 221. 
Chest of Wisdom, The, 60. 
China, chemistry in, 24-6. 
Chinese alchemy, 46, 47. 
Chlorine, 188, 189, 242. 
Cinnabar, preparation of, 105-6. 

production of, 58. 

Classification of the Elements, 263 -73 . 
cloud of arsenic, 37. 
Coagulation (solidification), 67. 
Cobalt, 5, in, 264. 
cohothar, 215. 
Collyrium, 47. 
Combining proportion, 248. 

volumes of gases, 252-3, 254. 
Combustion, 200-13. 

Hooke on, 155. 

in saltpetre, 155-6. 

Mayow on, 155-6, 158. 

theories of, 143 ff. 
Compendiun of Twelve Treatises, 64. 
Compositions ad tmgenda, 103. 
Composition of Alchemy, 86, 87. 
Compound radical, 276-7. 
Compounds, Proust on, 237. 
Conservation of Matter, 122. 
Copper, 4, 11-13, 73, 264. 

removal from gold, 80. 

removal from silver, 79, 80. 

oxide, used as hair darkener, 68. 

salts, blue colour with ammonia, 

sulphate, on electrochemical 
theory, 262. 

vitriol, 68. 
Coral, artificial, 14. 
Corks, use of, for stoppering, 15960. 
Cours de Chymie, 128, 130. 
Criminals, employed in Egyptian 
mines. 8 

Subject Index 


Crusades, 84. 

Cry of tin, 74. 

Crystals, structure of, 294-5. 

Cultivation of Gold, 82. 

Cupellation, 77, 79, 80. 

De Caelo, 16. 

De Caelo et Mundo, 78. 

Defence of Phlogiston , 211. 

De general ione et corruptione, 16. 

De Mineralibus, 91. 

Dephlogisticated air, 175-7, 182-6, 

204, 207, 208. 

Dephlogisticated marine acid, 188. 
De Re Metallica (De Metallis}, 77, 


De Rerum Natura, 21. 
Descensory, 58, 66. 
Dictionary of Chemistry, 221. 
Dictionnaire de Chirme, 150. 
Diffraction grating, 292-4. 
Distillation of sea- water, 68. 
Dualistic Theory, 258-63. 
Dyeing, 59. 

metals, 74, 9 r . 
Dyes, 274. 

Earth, 16-20. 
Egypt, chemistry in, 2-10. 
Elastic fluids, 220, 223. 
Electric battery, 259. 
Electrochemical Theory, 25863. 
Electrolysis, 259-62, 2869. 
Electrolytic dissociation, early criti- 
cism of, 289. 
theory of, 287-9. 
Siemens de Chymie, 128. 
Elements, Aristotelian, 16-20, 133-5, 


Boyle on, 137-8, 140. 

Lavoisier on, 140-2. 

Mellor on, 142. 

Paracelsan, 114. 

unknown, existence predicted, 270. 
Elixir, 25, 39, 44, 52, 67, 83. 
Empyreal air, 207. 
End of the Search, 82. 
Equivalent, 248. 
Essai de Statique Chimique, 236. 
Evaporation of the Divine Water that 

fixes Mercury (Zosimos), 35. 
Execution of Lavoisier, 212-13. 
Exhalations, 19, 57. 
Experience, Roger Bacon's interpre- 
tation of, 96. 

Experiment, Lavoisier's, 205-7. 
Experimental Researches in Electri- 
city, 286. 

Experimental temper, of Arabs, 86. 
Experiments on Magnesia Alba, 166. 
Explosives containing saltpetre, 104. 

Factitious Air, 178. 
Families, of elements, 264. 
Fermiers generaux, 199. 
Feuerluft, 188. 
Fire, 16-20. 
Fire-air, 188. 
Fixed air, 167, 179. 
fliiorum, 263. 
Formulae, 242-8, 280. 

of organic compounds, 278. 

structural, 281-3. 
Four Elements, 16-20, 133, 138. 
Fulminating gold, 131. 
Furnaces, The Book of, 60. 
Fusible subtances, 72. 

Galenical liquors, 116. 
Gas, invention of name, 121. 
Gas ptngue, 122. 
Gas silvestre, 122. 

Gases, conduction of electricity in, 

method of drying, 179. 

stored over mercury, 179. 
Gay-Lussac's Law, 252. 
Geometrical conception of atoms, 


Germanium, 272. 
Glass, 10. 

analysis of Pompeian, 14. 

'discovery' of, 98, 100. 

of antimony, 118. 

pliant, 100. 
Glass-blowing, 10. 
Glass-making, 13, 14. 
Glass-moulding, 10. 
Glauber's secret arnnioniacal salt, 1 95 . 
Gnosis, 33. 
Gnosticism, 33, 34. 
Gold, 5-10, 12, 73, 264. 

alchemical, tested by Albertus 
Magnus, 91. 

assaying of, 77. 

calcination of, 104-5. 

fulminating, 131. 

parting of from silver, 77, 105. 

purification of, 79, 80. 


Subject Index 

Gold-mine, plan of, 6. 

Golden Calf, i . 

Golden Fleece, i. 

Great Book of Properties, 106. 

Greece, 1524. 

Greek books, imported into Islam, 


fires, 104. 

Grotto del Cane, 122. 
guhlu, 14. 
Gunpowder, 24. 

Bacon's 'cipher', 97. 

early recipe for, 104. 
Gypsum, 12. 

plaster, 68. 

Haematite, 14, 80. 

Hair-dyes, 59. 

Handbook of Chemistry, 275. 

Harran, 48. 

hayuli, 46. 

Heat, part played by, in combustion, 


Helium, 296. 
Heterotopes, 300-1. 
Highly respirable air, 207. 
History of Chemistry (Thomson), 

(Kopp), 256. 

House of Wisdom (Baghdad), 52. 
Hydrochloric acid, 188. 
Hydrogen, 130, 149, 263. 

discovery of, 179- 

Hypostatical Principles, 134-5, 138. 
Hypothesis, Avogadro's, 253, 266, 

its importance, 257. 

latrochemistry, ii3ff. 
iksir, 46. See elixir. 
Illuminating ink, 59. 
immanakku, 14. 
Incendiary substances, 104. 
India, chemistry in, 26-7. 
Indium, 272. 
Inflammable air, 179. 
Invention of Verity, 60. 
Investigation of Perfection, 60. 
Iodine, 270, 273. 
'Ions, 288-9. 
Iron, 4, 5, 73, 264. 
Islam, chemistry in, 4184. 
Isomerism, 279. 

Jahiliyya, The, 43. 

Jardin des Plantes, see Jardin dn Roi. 

Jar din du Roi, 128, 189, 190-?. '198, 

208, 250. 

Journal dc Delametherie, 253. 
Jundi-Shapur Academy, 48. 

Kabbala, 108. 

Khem, 35. 

kibaltu, 15. 

Kit ab al-Fihrist, 52. 

krasis, 20. 

Kufa, foundation of, 49. 

kuhl, 14. 

knraja, 79. 

Laboratories, early chemical, 118. 
Laboratory, Berzelius's, 2412. 
Latin alchemical terms, adopted 

from Arabic, 1012. 
works of Geber, 60-3. 
works on alchemy, many spurious, 


Law of ConstantComposition, 236-7. 
of Multiple Proportions, 236-8. 
of Octaves, 266-8. 
of Partial Pressures, 224. 
of Reciprocal Proportions, 236, 239. 
of the Combination of Gases by 
j Volume, 251. 

' of the Conservation of Matter, 230, 

2 3 6 /. 
Laws ot Electrolysis, 286. 

Lead, 5, 74, 264. 

acetate, 37. 

isotopes of, 301. 

oxide, 13. 

Leyden Papyrus, 29-32, 103. 
Libellus de Alchimia, 91 . 
Liber igmum, 103, 104. 
Light, 263. 
Lime, 13, 264. 
Limestone, nature of, 167-9. 
Litharge, 37, 58, 148. 

Magic, 34. 
Magnesia, 264. 
magnesia alba, 167-8, 197. 
Malleus Maleficarum y 273. 
Manganese, 264. 

dioxide, 14, 59, 188. 
Manuscript, of Rouelle's lectures, 

Subject Index 

Mappae Clavicula, 103. 
Marble, 12. 
Marcasite, 14, 59. 
marhaSi, 15. 
Marine acid, 188. 
Mechanical mixture, 20, 21. 
Mercuric oxide, 78-9. 
Mercury, 73, 264. 

Bartholomew on, 100. 

from cinnabar, 37. 

preparation from minium (cinna- 
bar), 101. 

used in pneumatic trough, 163, 

179, 180. 

Mercury-sulphur theory. See sul- 
phur-mercury theory. 
Mercy, The Book of, 60. 
Meshed, 50. 

Metal industry, Babylonian, 15. 
Metallic calces, composition of, 207. 
Metallurgists, Egyptian, 310. 
Metals, acted upon by sulphuric acid 

constitution of, 57, 72, 73, 146. 

genesis of, 19. 
Meteorologica, 16, 19, 78. 
Methode de Nomenclature Chimique, 

214, 216. 
methridatic, 109. 
Minerals, Book on, 90. 
Minerals, classification of, 89, 90 

formation of, 72. 

genesis of, 19. 
Mines, Egyptian, 3. 
Minium, 177. 
mix is, 20. 
Moh's scale, 14. 
Molecule, 2537. 
Molybdenum, 264. 
murium, 263. 
Muslim Chemistry, review of, 82-4. 

Names, 'kitchen', ridiculed by 

Dumas, 215. 
namrutu, 14. 
Natron, 10, 38. 
natrun, 68. 

Natural History (Pliny), 27. 
Neo-Platonism, 33, 34. 
Neo-Platonists, 108, 114. 
New System of Chemical Philosophy, 

224, 230, 252. 
Nickel, 264. 
Nitre, 195. 

Nitric acid, 77, 207, 209. 

composition of, 1846. 

discovery of, 60. 
'Nitric acid' (nitric oxide), 238. 
Nitro-aerial spirit, 156, 158. 
Nitrous air, 209. 

ammomacal salt, 195. 

gas, 238. 

oxide, 238. 
Nomenclature, principles of, 215-17. 

revision of, 21317. 
nub (gold), 6. 
nub-en-mu, 9. 
nub-en-set, 9. 
Nucleus, 2967. 

Numbers, mystical powers of, 34. 
Nymphs, 1 14. 

Octaves, Newlands', 2668. 
Olefiant gas, 226, 228, 230, 238. 
Op ticks, 219. 
Opus Tertium, 94, 104. 
Organic analysis, 2745. 

Chemistry, rise of, 273-84. 

compounds, 2734. 
Ortus rnedicinae, 120. 
Oxalates of potassium, 228, 238. 
Oxygen, 24, 156, 208, 263. 

and phlogiston theories contrasted, 


Oxygen, explosion with hydrogen, 

theory, Lavoisier's claim to, 212. 
Oxymel, 52. 
Oxymuriatic acid, 242. 

Particles of Gold, 76. 

parzel, 15. 

parzillu, 15. 

Pearls, artificial, 10. 

Pelican, 214. 

Periodic System, 26873. 

anomalies in, 2723. 

Table, 271. 
Peripatetic theory, of the elements, 


Perizzites[? Metal-workers], 15. 
Persian influence, on alchemy in 

Islam, 46. 

Pharmacology, Persian, 67-8. 
Philosopher's stone, 39, 40, 109, 122, 

I2 4-. 
Philosophical Transactions, 178, 280. 


Subject Index 

Phlogiston. 146 ff., 179, 183, 1 88. 

Lavoisier's attack on, 210. 

negative weight of, 153. 

theory, 20, 58, 146-54, 169, 171-7. 

fall of, 197-213. 

Phosphorescent substances, 104. 
Phosphoric acid, 207. 
Phosphorus, 263. 

combustion of, 200 i . 
Physica Auscultatio, 78. 
Physical Chemistry, rise of, 284-9. 
Physica Subterranea, 144, 146. 
Platinum, 264. 
plombe rouge, 177. 
Pneumatic Chemistry, 158-63. 

trough, 121 . 

evolution of, 160-3. 
Polarity of atoms and groups, 261-3. 
Potassium, 261. 

carbonate, 68, 179, 216. 

sulphate, 194. 
powder of Algaroth, 215. 
precipitate per se, 177. 
prima materia, 16. 
Prime matter, 97. 
Principia, 220, 224. 
Principle acidifying, 208. 

oxygine, 208. 
Principles, Lemery's, 130. 

Paracelsan, 134. 
Probierbuechlein, 77. 
Properties of Things, On the, 98. 
purple of Cassius, 14. 
Pyrites, 15. 
Pyrolusite, 188. 

Qali, 68. 

qambar, 46. 

Qualities, Aristotelian, 16. 

doctrine of, 135. 

Quicklime, used as depilatory, 68. 
Quintessence, 109. 

Book of, 104. 

Radical Theory, Book of, 104, 276-7. 
Radioactivity, 290-1, 295-6, 301. 
Radium, 290, 299. 
emanation, 296. 
Radon, 296, 299. 

Rare gases, in Periodic System , 272-3 . 
Rays, 290-302. 
Realgar, 72. 

Recipe-book, thirteenth - century, 

Reduction of calces, 58. 
Refining-furnace, 80. 
Reflexions sur Phlogistique, 207. 
Refutation of alchemy, 74. 
Relative masses of molecules, 253-7, 
weights, 233. 

of atoms (Dalton), 226. 
Remedy, The Book of the, 70, 91. 
Respiration, 175. 
Rome, chemistry in, 27-9. 
Rotisserie de la Heine Pedauque, 114. 
Rouen-green, 105. 

Sabians, 48. 
sadanu, 14. 

Sage's Step, The, 77-80. 
sal Alembroth, 215. 
Salamanders, 114. 
Sal-ammoniac, 72, 195. 
sal nit rum, 156. 
Salt, middle, 194. 

neutral, 194-6. 

'salty', 194. 
Saltpetre, 188. 
Salts, 72. 

acid, 195-6. 

perfect, 195. 

Rouelle's work on, 194-6. 
sandarach, 14, 37. 
Sapphire, 14. 
Sausages, Kekule's, 281. 
Sceptical Chymist, 137, 140. 
Sciences, handmaids of Theology, 


Scientific method, 134. 
Sea-salt, 195. 
Secrets, Book of, 64. 
Seventy, The Book of, 60 i . 
shadana, 14. 
Shi'ites, 50. 

Sicily, a centre of learning, 84. 
Silica, 13, 122, 264. 
Silicic acid, 68, 122. 
Silver, 12, 73, 264. 

chloride, 196. 

extraction by amalgamation, 77. 

recovery by amalgamation, 80. 

separation from lead, 79. 
Silver-mountains [? Taurus], 12. 
Simple substances, table of, 2634. 
Sindu arqu, 14. 
siprn, 14. 
Soap, 10. 
Soda, 58. 

Subject Index 

Sodium carbonate, 68. 

discovery of, 261. 
"sesqui-carbonate, 10. 

sulphate, on electrochemical 

theory, 262-3. 
Solutions, nature of, 286-9. 

physical properties of, 2869. 
Song of Solomon, 2. 
Souls, 59. 
Spain, transmission of knowledge in, 

84, 86, 87. 
Specific gravity, 83. 
Specimen Becherianum, 146. 
Spirit of salt, 179, 1 88. 
Spirits, 59. 

Stannic chloride, 118. 
Steel, 59. 

Stockholm Papyrus, 29-32. 
Stones, 72. 

Structure of the Atom, 290-302. 
Sulphur, 72, 263. 

dioxide, bleaching action of, 1 1 1 . 
Sulphuric acid, 118, 149, 207, 209. 

action on metals, 179. 
Sulphur-mercury theory, 57, 81, 83, 

90, 97, 100, 11415, 118, 143. 
Sulphurs, 72. 
Sum of Perfection, 60 i . 
Summary of a Course of Chemical 

Philosophy, 257. 
Sylphs, 114. 
Symbols, 216, 242-8. 

Dalton's, 226, 243. 

of Ber/ehus, criticized by Dalton, 


Sympathetic properties, 34. 
Synthesis, 20, 282-3. 
Syrian translators, 48. 
Syrup of violets, 196. 
System of Chemistry, 224. 

Tabarmaq of Khurasan, 75. 
tabashir, 68. 
Tao-ism, 24. 

Technical Tradition, 98-106. 
Tellurium, 270, 273. 
terra lapida, 146. 
terra mercurialis, 146. 
terra pinguis, 146. 
Testament of Geber, 60. 
Textbook of Organic Chemistry, 280. 
Theorie des Proportions Chimiques, 

Theory of Substitution, 277. 

of Types, 277. 
theriac, 109. 
Thorium, radioactive degradation of 


Timaeus, 23. 
Tin, 5, 73, 264. 

calcination of, 201-4. 

cry of, 74. 

origin of, 38. 

oxide, 14. 

Tincture of the Philosophers, no. 
Translators, of Arabic works, 84-6. 
Transmission of alchemy to Islam, 


Transmutation, 19, 24, 36, 83, 103, 

disbelief in, 63. 

scepticism concerning, 73-6, 90, 91. 
Treatise on Chemistry, 200. 
Treatise on Instruments and Furnaces 

(Zosimos), 35. 
Treatise on the Alembic with Three 

Beaks (Zosirnos), 35. 
Tria prima, 114, 118, 120, 133, 134, 


Triads, Dobereiner's, 264-5. 
Tungsten, 264. 
turbith mineral, 215. 
Tus, 50. 
Types, 277. 

uhulu, 14. 
Umayyads, 50. 
Universal Matter, 130. 
Uranium, radioactive degradation of, 

Valency, 280. 

indication of, 281. 

of carbon, 280. 
Vegetable Staticks, 161. 
Verdigris, preparation of, 105. 
Vermilion, 105. 
Virtue, Book o/(Zosimos), 35. 
Vital air, 207. 

force, 275. 
Vitriol, 72, 73, 103. 

oil of, 130-1 

Vitriolated tartar, 194-5. 
Vitriols, in. 
Volatile alkali, 195. 
Voltaic pile, 259. 
Volumetric analysis, 259. 

Subject Index 

Water, 16-20. 

as sole primitive element, 120. 

composition of, 180-4. 

electrolysis of, 259. 

formula of, 232-3, 256. 
Water-bath, i. 
Water-glass, 122. 
Waterproofing cloth, 59. 
Weighing, Arab accuracy in, 83. 
Weight, oldest known, 12. 
White lead, 37,68. 

] X-ray spectrometer, 292-4. 

spectrum, 294. 
X-rays, 291 ff. 

Yang, 24. 
yin, 24. 

Zarnikh, 46. 

Zeitschnjt fur physikahscJie Chemie t 

Zinc, in, 264.